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OUTLINES 

OF 

PHYSIOLOGICAL  PSYCHOLOGY 


PROFESSOR    LADD'S    WORKS. 


INTRODUCTION  TO  PHILOSOPHY.  An  Inquiry 
after  a  Progressive  Rational  System  of  the  Principles  of  the 
Particular  Sciences  in  their  Relation  to  Ultimate  Reality, 
i  vol.,  8vo,  $3.00. 

ELEMENTS  OF  PHYSIOLOGICAL  PSYCHOLOGY. 

A  Treatise  of  the  Activities  and  Nature  of  the  Mind,  from 
the  Physical  and  Experimental  Point  of  View.  With  nu- 
merous illustrations.  $4.50. 

WHAT  IS  THE  BIBLE?  An  Inquiry  of  the  Origin  and 
Nature  of  the  Old  and  New  Testaments  in  the  Light  of 
Modern  Biblical  Study,  izmo.  $2.00. 

THE    DOCTRINE    OF    SACRED    SCRIPTURE.      A 

Critical,  Historical,  and  Dogmatic  Inquiry  into  the  Origin 
and  Nature  of  the  Old  and  New  Testaments.  2  vols., 
8vo,  $7.00. 

THE  PRINCIPLES  OF  CHURCH  POLITY.  Crown 
8vo,  $2.50. 


OUTLINES 


OF 


PHYSIOLOGICAL  PSYCHOLOGY 


A   TEXT-BOOK  OF  MENTAL  SCIENCE 


FOR 


ACADEMIES  AND  COLLEGES 


BY 

GEORGE  TRUMBULL  LADD 

jj 

PROFESSOR  or  PHILOSOPHY  IN  YALE  UNIVERSITY 


NEW  YOKK 

CHARLES   SCRIBNER'S   SONS 
1891 


BIOLOGY 

UBRARt 

6 


COPYRIGHT,  1890 
BY  CHARLES  SCRIBNER'S  SONS 


PREFACE. 


IN  the  early  part  of  1887  I  published  the  results  of  sev- 
eral years  of  research,  in  a  book  entitled  "  Elements  of 
Physiological  Psychology."  The  very  gratifying  reception 
almost  immediately  given  to  this  work  showed  an  extended 
and  profound  interest  in  the  experimental  and  physiological 
study  of  mental  phenomena.  The  signs  of  this  interest 
have  continued  unabated  until  the  present  time ;  and  the 
book  has  been  widely  adopted,  both  in  this  country  and 
abroad,  for  private  reading  and  for  the  instruction  of 
classes. 

Although  the  "  Elements,  etc."  did  not  enter  into  the 
detailed  history  of  discoveries  and  discussion  of  theories  in 
the  field  of  physiological  psychology,  it  was  necessarily 
somewhat  voluminous  and  technical.  For  it  aimed  to  give 
a  summary  of  the  entire  field ;  and  thus  to  render  accessible 
the  data  and  conclusions  to  be  found,  separated,  only  in 
scores  or  hundreds  of  larger  and  smaller  monographs. 

Almost  immediately  the  demand  arose  for  a  smaller  and 
less  technical  book,  which  should  be  adapted  to  aid  the 
teacher  with  classes  less  mature,  or  able  to  afford  less  time 
to  the  subject.  The  present  volume  has  been  written  for 
the  express  purpose  of  meeting  this  demand.  It  is  not, 
however,  a  mere  abridgment  or  revision  of  the  larger  work. 
While  it,  like  the  larger  work,  surveys  the  entire  field,  it 
omits  all  details,  discussions,  and  references,  which  —  how- 
ever valuable  for  the  purposes  of  more  thorough  mastery 

43280 


vi  PKEFACE. 

—  are  likely  to  embarrass  beginners  of  more  limited 
patience  and  ability.  The  Parts  (I.  and  III.)  which 
treated  of  the  nervous  mechanism  and  of  the  nature  of 
mind  as  related  to  the  body,  have  been  in  this  volume 
relatively  much  abbreviated;  while  the  Part  (II.)  which 
treated  of  the  phenomenal  relations  existing  between  the 
excited  organs-  and  mental  phenomena,  has  been  relatively 
somewhat  expanded.  Here  considerable  new  material  — 
especially  in  the  chapter  on  "  Consciousness,  Memory,  and 
Will "  —  has  been  added.  I  have  thus  aimed  to  furnish 
a  complete  and  yet  compact  text-book  for  the  briefer  study 
of  mental  phenomena  from  the  experimental  and  physio- 
logical point  of  view. 

In  carrying  out  the  general  aim  of  this  manual,  both 
pupil  and  teacher  have  been  kept  in  view.  The  material 
has  been  arranged  so  as  to  adapt  it  for  learning  with  the 
least  unnecessary  expenditure  of  strength  and  time.  It  is 
my  hope  also  to  have  succeeded  in  providing  those  who 
give  instruction  with  a  book  which  can  be  successfully 
taught. 

Some  equipment  of  apparatus  is  desirable,  if  not  abso- 
lutely indispensable,  for  the  most  effective  instruction  in 
physiological  psychology.  This  equipment  need  not,  how- 
ever, be  large  or  expensive.  A  set  of  models  of  the  brain 
(I  recommend  the  Bock-Steger),  a  few  charts,  a  judicious 
selection  of  histological  preparations,  a  machine  for  mixing 
color-sensations,  etc.,  are  of  great  assistance. 

For  the  use  of  teachers,  of  more  advanced  or  mature 
pupils,  and  of  such  readers,  generally,  as  can  command 
the  patience  and  the  time,  the  "  Elements  of  Physiological 
Psychology  "  is  still  to  be  preferred.  For  most  teachers 
who  adopt  the  present,  smaller  treatise  as  a  text-book  in 
the  class-room,  the  larger  work  will  be  found  indispensable 
for  their  private  use.  The  latter  is  still,  in  most  of  the  sub- 
ordinate topics,  well  abreast  of  the  very  latest  researches. 


PREFACE.  Vii 

And  if  its  material  is  constantly  supplemented  by  those 
notices  of  new  discoveries  for  which  one  must  look  to 
periodical  literature  (e.g.  the  American  Journal  of  Psy- 
chology), it  will  serve  to  keep  even  the  teacher  who  is  not 
a  specialist  in  the  lines  of  physiology  and  psycho-physics, 
in  advance  of  his  classes. 

Having  been  for  some  years  a  teacher  of  this  subject,  I 
am  well  aware  what  are  the  difficulties  of  presenting  it. 
But  I  have  also  learned  that  the  rewards  which  follow  the 
overcoming  of  those  difficulties  are  correspondingly  great. 
It  will  be  a  matter  of  great  interest  to  me,  therefore,  to 
receive  suggestions  and  encouragement  from  those  of  my 
fellow-teachers  who  may  avail  themselves  of  this  book. 


GEORGE  TRUMBULL  LADD. 


YALE  UNIVERSITY,  NEW  HAVEN, 
Nov.,  1890. 


TABLE   OF  CONTENTS. 


PAGES 

INTRODUCTION.    NATURE  OF  PHYSIOLOGICAL  PSYCHOLOGY        1-10 

CHAPTER  I. 
SUBSTANCE  OF  THE  NERVOUS  SUBSTANCE 11-30 

CHAPTER  II. 
STRUCTURE  OF  THE  SPINAL  CORD  AND  BRAIN      ....      31-73 

CHAPTER  III. 
STRUCTURE  OF  THE  ORGANS  OF  SENSE  AND  MOTION    .     .    74-102 

CHAPTER  IV. 
DEVELOPMENT  OF  THE  NERVOUS  SYSTEM 103-115 

CHAPTER  V. 
GENERAL  PHYSIOLOGY  OF  THE  NERVES 116-134 

CHAPTER  VI. 
REFLEX  AND  AUTOMATIC  NERVOUS  FUNCTIONS    ....  135-157 

CHAPTER  VII. 

MECHANICAL  THEORY  OF  THE  NERVOUS  SYSTEM      .     .     .  158-176 

ix 


X  TABLE   OF  CONTENTS. 

CHAPTER  VIII. 

SENSORY    AND    MOTOR    FUNCTIONS    OF    THE    CEREBRAL       PAGES 
HEMISPHERES 177-195 


CHAPTER  IX. 

SENSORY    AND    MOTOR    FUNCTIONS    OF    THE    CEREBRAL 

HEMISPHERES—  Continued  .  .  196-227 


CHAPTER  X. 
THE  QUALITY  OF  SENSATIONS 228-253 

CHAPTER  XL 
THE  QUALITY  OF  SENSATIONS—  Continued 254-270 

CHAPTER  XII. 
THE  QUANTITY  OF  SENSATIONS 271-289 

CHAPTER  XIH. 
PERCEPTION  BY  THE  SENSES 290-321 

CHAPTER  XIV. 

PERCEPTION  BY  THE  SENSES — Continued     .    .    .    .    .    .  322-360 

CHAPTER  XV. 
TIME-RELATIONS  OF  MENTAL  PHENOMENA  ......  361-380 

CHAPTER  XVI. 
FEELINGS,  EMOTIONS,  AND  MOVEMENTS  .     .         ....  381-413 


TABLE   OF   CONTENTS.  XI 

CHAPTER   XVII. 

PAGES 

CONSCIOUSNESS,  MEMORY,  AND  WILL 414-444 

CHAPTER  XVIII. 
AGE,  SEX,  AND  TEMPERAMENT 445-461 

CHAPTER  XIX. 
CONNECTION  OF  BODY  AND  MIND 462-477 

CHAPTER  XX. 
THE  NATURE  OF  MIND  ...          ....  .  478-499 


INDEX 501-505 


PHYSIOLOGICAL   PSYCHOLOGY. 

INTRODUCTION. 
NATURE   OF  PHYSIOLOGICAL  PSYCHOLOGY. 

THE  satisfactory  definition  of  any  science  is  often  one  of 
the  latest  and  most  difficult  achievements  of  that  science. 
Our  definition  of  the  particular  science  which  we  intend 
to  consider  must,  therefore,  be  understood  as  preliminary. 
It  involves  positions  upon  various  disputed  questions  which 
the  beginner  is  quite  unable  to  comprehend ;  and  it  must 
be  allowed,  in  a  measure,  to  rely  upon  the  course  of  the 
following  investigation  for  its  explanation  and  defence. 
Everything  cannot  be  said  at  once.  Terms  must  be  freely 
used,  the  meaning  of  which  will  be  made  clear  only  by 
their  use ;  and  answers  to  later  inquiries  will  sometimes 
be  implied  in  what  is  said  upon  inquiries  that  are  earliest 
raised. 

It  is  plain  that  a  correct  conception  of  Physiological 
Psychology  involves  some  special  knowledge  of  those  two 
sciences  whose  names  are  combined  in  the  term  itself. 
These  are,  of  course,  Psychology  and  Physiology.  It  is 
also  plain  that  a  peculiar  relation  is  assumed  to  exist 
between  certain  of  the  results  obtained  by  the  study  of 
these  two  sciences ;  otherwise  they  could  not  properly  be 
combined  in  one  term.  It  is  furthermore  suggested  by 
this  compound  name,  that  the  science  which  furnishes  the 
noun  —  namely,  psychology  —  defines  the  end  which  we 
desire  to  reach ;  while  the  science  which  furnishes  the 


2  PHYSIOLOGICAL   PSYCHOLOGY. 

adjective  —  namely,  physiology  —  prescribes  the  means 
which  we  are'  to  employ.  This  suggestion  we  shall  find 
to  be  confirmed  by  our  subsequent  investigations. 

Definition  of  Pyschology.  —  It  was  for  a  long  time  custo- 
mary to  define  psychology  as  "  the  science  of  the  human 
soul."  Sometimes  the  definition  went  so  far  as  to  add  that 
the  soul,  "  as  the  real  foundation  of  the  spiritual  life,"  or 
as  "the  subjective  spirit,"  is  the  "subject-matter  of  psy- 
chology." Of  late,  however,  serious  objections  have  been 
raised  against  every  such  definition.  It  has  been  com- 
plained that  the  word  "  soul,"  although  its  German  equiv- 
alent is  freely  employed  in  biological  and  physiological 
treatises,  cannot  be  sufficiently  kept  free,  for  scientific  pur- 
poses, from  theological  and  other  prejudices.  The  word 
"  mind,"  which  had  originally  a  much  narrower  signifi- 
cance, has  therefore  been  substituted  in  the  greater  number 
of  English  works  on  psychology.  Thus  Mr.  Sully  defines 
psychology  as  "our  general  knowledge  of  mind  reduced 
to  an  accurate  and  systematic  form." 

Other  objections  to  the  customary  definition  of  psychol- 
ogy are  not  met,  however,  by  exchanging  the  word  "  soul " 
for  the  word  "  mind."  Thus  it  is  said  that  both  words  are 
often  used  so  as  to  conceal  the  unproved  assumption  that 
mind  or  soul  is  an  independent  entity ;  whereas  it  is  the 
business  of  the  science  of  psychology  to  prove,  if  it  can, 
the  existence  of  such  an  entity.  Biology,  which  aims  to 
extend  its  researches  so  as  to  include  mental  as  well  as 
other  vital  phenomena,  sometimes  asserts  that  it  wishes  the 
opportunity  to  explain  what  occurs  in  consciousness  without 
making  use  of  any  assumptions.  Some  writers,  then,  have 
gone  so  far  as  to  advocate  "  psychology  without  a  soul." 
Others,  on  the  contrary,  have  thought  they  found  proof, 
in  the  complex  phenomena  of  human  life,  of  both  an  "  ani- 
mal "  and  a  "  rational "  soul. 

In  order  to  the  intelligent  pursuit  of  physiological  psy- 


NATURE   OF   PHYSIOLOGICAL    PSYCHOLOGY.  3 

chology,  it  is  necessary  to  notice  the  foregoing  objections 
only  very  briefly.  Our  view  of  the  best  preliminary  de- 
scription of  the  nature  of  psychology  is  as  follows :  It  is 
expedient,  as  far  as  possible,  to  avoid  all  controversy  at 
the  beginning  of  our  scientific  investigation.  We  should 
therefore  be  willing,  where  this  can  be  done,  to  dispense  with 
controverted  words  in  forming  our  fundamental  concep- 
tions. It  is  also  more  satisfactory,  from  the  purely  scien- 
tific point  of  view,  to  have  the  definition  include  only  a 
description  of  that  particular  group  of  phenomena  which 
it  is  the  business  of  the  science  itself  to  explore.  In  this 
way,  then,  we  define  psychology  with  reference  to  its  primary 
problem,  which  is,  the  description  and  explanation  of  the 
states  of  human  consciousness,  as  such. 

If  the  term  "  sentience  "  seems  preferable  to  conscious- 
ness, it  must  be  understood  as  equivalent  to  consciousness 
in  the  broader  sense  of  the  latter  word.  We  may  then  say 
that  psychology  is  the  science  which  describes  and  explains 
the  phenomena  of  the  sentient  life  of  man. 

This  definition  plainly  implies  an  acquaintance,  already 
gained,  with  a  certain  class  of  phenomena.  These  are  the 
phenomena  of  consciousness.  What  it  is  "  to  be  conscious," 
and  what  is  that  peculiar  character  which  belongs  to  all 
phenomena  of  consciousness,  as  such,  can  never  be  defined. 

It  would  be  inconvenient  and  unnecessary  —  not  to  say 
impossible  —  to  refuse  to  speak  of  the  "  soul  "  or  "  mind  " 
simply  through  fear  of  unscientifically  making  the  assump- 
tion that  some  such  entity  really  exists.  In  all  languages, 
and  in  the  every-day  use  of  them  all,  men  in  expressing 
their  states  of  consciousness,  as  well  as  in  addressing  their 
fellows,  employ  such  terms  as  "  I  "  or  "  me,"  and  "  thou" 
and  "  he,"  or  "  it."  But  all  these  words  imply  some  kind 
of  reference  to  a  subject  of  the  phenomena  of  conscious- 
ness ;  they  also  imply  a  contrast  between  this  subject  and 
other  subjects  to  which  other  phenomena  are  attributed. 


4  PHYSIOLOGICAL   PSYCHOLOGY. 

In  all  the  earlier  part  of  our  investigation,  whenever  we 
use  the  word  "  mind  "  or  "  soul,"  we  wish  to  imply  no 
more  than  all  men  inevitably  mean  whenever  they  say 
"  I "  see,  or  think,  or  feel,  or  purpose,  this  or  that.  It  is 
the  seeing,  thinking,  feeling,  and  purposing,  etc.,  as  states 
of  consciousness,  with  this  possible  reference  to  a  subject 
of  them  all  (states  of  consciousness  as  subjective),  which 
constitute  the  field  to  be  explored  by  psychology. 

Definition  of  Physiology. — The  science  which  is  to  be 
combined  with  psychology  in  our  investigations  is  human 
physiology.  This  is  the  science  of  the  functions  of  the 
human  physical  organism.  Its  modern  study  implies  an 
acquaintance  with  several  other  sciences  with  which  it 
is  closely  allied,  or  upon  which  it  is  dependent.  These 
are  molecular  physics  and  chemistry,  as  related  to  the 
structure  and  changes  of  the  tissues  of  plants  and  ani- 
mals ;  biology,  including  the  allied  phenomena  of  plant  life  ; 
embryology  and  the  general  theory  of  development ;  and 
gross  and  special  microscopic  anatomy,  or  histology.  It 
is  only,  however,  with  a  small  part  of  this  vast  domain  that 
physiological  psychology  has  directly  to  deal.  Its  chief 
concern  is  with  the  structure  and  functions  of  the  human 
nervous  system. 

Definition  of  Physiological  Psychology.  —  It  has  already 
been  implied  that  our  conception  of  this  science  is  depend- 
ent upon  the  way  in  which  we  understand  the  two  sciences 
to  be  combined  in  its  pursuit.  But  the  science  of  psychol- 
ogy furnishes  the  end  or  final  purpose  of  our  researches. 
In  other  words,  we  aim  to  describe  and  explain  the  states 
of  human  consciousness,  as  such.  On  the  other  hand, 
physiology  furnishes  the  peculiar  means  to  be  employed, 
—  the  point  of  view  held  in  our  description,  and  the 
method  and  source  of  our  explanation.  We  study  the 
subject-matter  indicated  by  the  noun ;  but  we  study  it  by 
use  of  the  somewhat  peculiar  means  and  ways  of  approach 


NATURE   OF    PHYSIOLOGICAL   PSYCHOLOGY.  5 

indicated  by  the  adjective.  We  may,  then,  define  physi- 
ological psychology  as  the  science  of  the  phenomena  of 
human  consciousness  in  their  relations  to  the  structure  and 
functions  of  the  nervous  system.  It  is  psychology,  because 
it  is  the  science  of  the  human  mind,  or  soul ;  it  is  phys- 
iological psychology,  because  it  regards  the  mind  as  stand- 
ing in  peculiar  relations  to  the  bodily  mechanism. 

Method  of  Physiological  Psychology.  —  In  its  method  this 
compound  science  necessarily  partakes  of  the  character- 
istics of  the  two  sciences  which  enter  into  it.  But  these 
two  sciences  differ  somewhat  widely  in  respect  to  their 
long-established  methods.  They  also  differ  in  their  very 
nature  in  such  a  way  as  to  make  necessary  a  difference  of 
method  in  their  pursuit.  It  has  always  been  held  by  a 
great  majority  of  its  students  that  the  method  of  psy- 
chology is  necessarily  what  is  known  as  "  introspective." 
But  there  can  be  no  doubt  that  the  method  of  physiology 
is  one  of  external  observation  and  experiment;  since 
physiology  is  a  physical  science  and  has  to  determine 
external  facts  of  the  structure,  development,  and  functions 
of  a  physical  mechanism.  It  is  not  strange,  therefore,  that 
doubts  and  even  disputes  have  arisen  as  to  the  possibility 
of  combining  these  two  methods,  and  as  to  the  proper  way 
of  making  the  combination,  in  case  it  is  to  be  made  at  all. 
These  doubts  and  disputes  are,  however,  for  the  most  part, 
unimportant. 

The  method  to  which  psychology  has,  from  time  almost 
immemorial,  appealed  is,  as  has  been  said,  introspection,  or 
self -consciousness.  The  exhortation  given  to  the  student 
of  mental  phenomena  is,  accordingly,  made  to  run  as  fol- 
lows: "Would  you  know  what  it  is  to  see,  to  hear,  to 
think,  to  feel,  to  desire,  to  will  ?  Then  look  within  your- 
self and  find  the  answer  there."  To  answer  such  ques- 
tions, inspect  within  (m£ro-spect) ;  to  know  what  is  the 
meaning  of  consciousness,  in  any  of  its  varied  forms,  be 


6  PHYSIOLOGICAL   PSYCHOLOGY. 

se(/-conscious,  or  aware  of  the  states  of  consciousness  as 
immediately  known  to  be  your  own.  But  like  the  defini- 
tion of  psychology,  this  conception  of  its  method  has  of 
late  been  much  called  in  question,  and  its  lack  of  scientific 
character  as  well  as  its  general  unfruitfulness  have  been 
exposed. 

What  view,  then,  shall  we  take  of  the  use  of  introspec- 
tion in  psychology,  and  more  particularly,  in  physiological 
psychology  ?  Now  there  should  be  no  mystery  or  arrogant 
assumption  about  such  words  as  "  science  "  and  "  scientific 
method."  Science  is  knowledge  —  real,  verifiable,  syste- 
matic. Scientific  method  is  nothing  but  the  way  of  arriv- 
ing at  such  knowledge.  In  physiological  psychology,  as  a 
science,  any  way  of  arriving  at  genuine  knowledge  is  jus- 
tifiable ;  all  ways  of  arriving  at  such  knowledge  should  be 
diligently  and  skilfully  employed.  But  the  phenomena 
which  we  must  somehow  know,  in  order  to  describe  and 
explain  them,  are  states  of  consciousness;  and  states  of 
consciousness,  as  primary  facts,  can  be  ascertained  in  no 
other  way  than  in  and  by  consciousness  itself.  This  way 
of  ascertaining  these  facts  is  introspection.  Introspection 
is,  therefore,  not  only  a  legitimate  but  it  is  an  indispen- 
sable method  of  physiological  psychology.  To  object  to 
it,  so  far  forth,  is  not  only  inexpedient  and  useless,  but  is 
even  absurd. 

Psychology  as  a  science,  however,  requires  not  only  that 
we  should  ascertain  by  introspection  what  the  states  of 
consciousness,  as  primary  facts,  actually  are,  but  also  that 
we  should  explain  these  facts  and  their  relations  to  one 
another  in  the  life  of  the  mind.  Such  explanation  requires 
at  least  two  things  :  these  are,  the  analysis  of  the  states 
into  their  simplest  factors,  and  the  discovery  of  the  law^s 
under  which  the  states  are  related  to  each  other  and  to  all 
the  conditions  on  which  they  depend.  Our  adult  states 
of  consciousness  furnish  the  problems  to  psychology ;  they 


NATURE  OF  PHYSIOLOGICAL  PSYCHOLOGY.  7 

are  its  primary  facts,  the  admitted  data  from  which  it 
takes  its  start.  But  they  are  all,  as  states,  exceedingly 
complex,  and  involve  numerous  factors.  Self-consciousness 
can  no  more  discover  all  the  factors  which  have  united  to 
form  these  states  than  simple  external  observation  can 
analyze  a  portion  of  water  into  its  constituent  oxygen  and 
hydrogen  gases.  Especially  is  it  true  that  few  of  the 
antecedent  and  accompanying  conditions  of  these  complex 
states  of  consciousness  can  be  discovered  by  introspection. 
Introspection,  therefore,  can  never  serve  as  the  sole  method 
for  establishing  a  science  of  psychology. 

Moreover,  those  antecedent  or  accompanying  conditions 
of  the  states  of  consciousness,  which  physiological  psy- 
chology particularly  endeavors  to  discover,  are  the  struc- 
ture and  functions  of  the  nervous  system.  About  these 
matters  introspection  can,  as  a  rule,  tell  us  nothing 
whatever.  The  physical  science  of  physiology,  with  its 
method  of  external  observation  and  experiment,  must 
be  relied  upon  to  describe  such  conditions  of  mental  phe- 
nomena. 

It  is  obvious,  then,  how  physiological  psychology  must 
combine  the  two  methods  which  belong  to  the  two  sciences 
on  which  it  depends.  Introspective  psychology  must  fur- 
nish us  with  the  description  of  those  complex  states  of  con- 
sciousness, as  such,  which  it  is  desired  to  explain.  These 
furnish  the  problems  to  be  solved.  Physiology,  on  the 
other  hand,  must  be  relied  upon  for  a  description  of  the 
living  and  active  nervous  system,  regarded  as  giving  con- 
ditions to  the  origin  and  character  of  the  states  of  con- 
sciousness. Physiological  psychology,  therefore,  attempts 
to  bring  the  two  orders  of  phenomena,  those  called  mental 
and  those  belonging  to  the  nervous  system,  face  to  face. 
It  considers  them  as  mutually  related ;  it  endeavors,  as  far 
as  possible,  to  unite  them  in  terms  of  a  uniform  character, 
under  law.  Its  method  is  to  explain  the  phenomena  of 


8  PHYSIOLOGICAL   PSYCHOLOGY. 

man's  sentient  life  as  correlated  with  the  life  and  growth 
and  action,  under  stimuli,  of  his  nervous  system. 

Divisions  of  the  Subject.  —  The  different  chapters  of  this 
book  fall  under  three  main  divisions.  We  shall  first  con- 
sider the  structure  and  functions  of  the  nervous  system 
from  the  modern  mechanical  point  of  view.  In  these  ear- 
lier chapters  we  must  rely  upon  the  method  of  external 
observation  and  experiment  as  employed  by  the  modern 
science  of  psychology.  Our  object  will  be  to  give  a  clear 
picture  in  outlines  of  what  the  nervous  system  of  man  is, 
and  of  how  it  acts  in  response  to  the  different  forms  of 
stimuli  which  excite  or  irritate  it.  This  work  requires 
little  reference  to  states  of  consciousness  or  to  the  nature 
of  the  mind.  We  shall,  in  the  main,  consider  the  nervous 
-system  as  a  purely  physical  mechanism.  Yet  even  in  these 
chapters  certain  important  considerations  bearing  upon  the 
nature  of  the  mind  and  its  relations  to  its  bodily  basis  will 
indirectly  come  into  view. 

The  next  eleven  chapters  (VIII.-XVIII.)  may  be  con- 
sidered as  constituting  the  second  or  main  division  of  the 
book.  In  these  chapters  the  various  relations  which  the 
science  of  physiological  psychology  has  discovered  between 
the  states  of  conscious  mind  and  the  conditions  of  the 
excited  nervous  system,  are  presented  in  order.  Such 
relations  may  conveniently  be  considered  under  three  gen- 
eral groups  or  classes.  The  first  group  comprises  the 
relations  which  can  be  established  between  the  condition 
and  activity  of  the  higher  nervous  centres  and  the  phe- 
nomena of  conscious  sensation  and  motion.  The  principal 
question  raised  under  this  head  concerns  the  so-called 
"  localization  of  function  "  in  the  hemispheres  of  the  brain. 
The  second  group  of  relations  includes  the  phenomena 
with  which  psycho-physics  (in  the  more  precise  use  of  the 
term)  attempts  to  deal.  Such  are  the  relations  which 
exist  between  the  quality,  quantity,  combination,  and  time- 


NATURE   OF   PHYSIOLOGICAL   PSYCHOLOGY. 

order  of  the  various  stimuli  which  irritate  the  nervous 
system,  and  the  kind,  amount,  composite  result,  and  time- 
relations  of  the  mental  phenomena.  A  third  class  of 
relations  considers  mind  and  body  as  dependent  upon  dif- 
ferences of  age,  sex,  race,  etc. 

At  the  close  of  the  more  strictly  scientific  discussions 
of  the  book,  we  shall  be  in  position  to  verify  certain  con- 
clusions as  to  the  nature  of  the  human  mind,  and  as  to  its 
general  connection  with  the  bodily  organism.  Some  of 
the  considerations  introduced  at  this  point  will  be  of  the 
kind  ordinarily  known  as  "metaphysical."  We  consider 
it  scientific  to  postpone  these  questions,  as  well  as  all 
assumptions  bearing  upon  them,  until  we  have  candidly 
and  thoroughly  discussed  the  related  phenomena  and  the 
laws  (or  uniform  ways)  of  their  relation.  But  we  also 
hold  that  psychology,  even  when  it  employs  the  physi- 
ological method,  has  the  right,  and  is  under  obligation,  to. 
suggest  and  defend  true  conclusions  as  to  the  nature  of 
the  mind. 

Benefits  of  the  Study.  —  It  has  been  shown  that  physiolog- 
ical psychology  can  scarcely  claim  to  be  an  independent 
science,  or  even  a  separate  and  definite  branch  of  general 
psychology.  It  is,  nevertheless,  a  most  interesting,  sug- 
gestive, and  productive  way  of  studying  mental  phe- 
nomena. For  a  long  time  the  so-called  "  old  psychology," 
as  pursued  by  the  introspective  and  metaphysical  methods, 
made  little  or  no  advance.  In  a  single  generation,  as  pur- 
sued by  the  experimental  and  physiological  methods,  the 
science  of  psychology  has  been  largely  reconstructed. 

The  modern  science  of  man  emphasizes  the  necessity  of 
studying  his  nature  and  development  as  that  of  a  living 
unity.  Man  is  known  as  the  head  of  a  series  of  physical 
and  psychical  existences.  Only  by  considering  him  in  this 
way  can  we  have  a  trustworthy  and  adequate  picture  of  his 
mental  life  and  mental  evolution.  Such  a  consideration 


10  PHYSIOLOGICAL  PSYCHOLOGY. 

the  psychology  which  relies  solely  upon  introspection  and 
metaphysical  speculation  is  unable  to  furnish.  The  actual 
achievements  of  the  new  science  of  physiological  psychol- 
ogy —  though,  of  course,  still  including  many  uncertain- 
ties and  leaving  many  gaps  to  be  filled  —  are  a  sufficient 
justification  of  its  demands  upon  all  students  of  the  human 
mind.  Further  proof  of  the  benefits  of  its  study  we  con- 
fidently leave  to  the  test  of  the  student's  experience. 


CHAPTER   I. 

SUBSTANCE   OF   THE  NERVOUS   SYSTEM. 

CHEMISTRY  and  the  microscope  have  succeeded  fairly 
well  in  analyzing  the  substance  of  the  human  nervous 
system.  For  this  purpose  it  is  safe,  within  certain  limits, 
to  direct  our  observation  and  experiment  upon  the  lower 
animals,  and  to  draw  inferences  from  them  which  will 
apply  to  the  case  of  man.  The  chemical  constituents  and 
minute  structure  of  the  elements  which  compose  all  ner- 
vous substance  are  largely  the  same.  In  describing  these 
matters,  it  is  not,  then,  so  necessary  to  pay  strict  attention 
to  the  specific  animal  form  from  which  the  substance  is 
derived.  It  is  the  way  in  which  the  elements  are  com- 
bined into  organs,  and  the  development  and  elaboration 
of  function  as  dependent  upon  these  organs,  which  con- 
stitute the  marked  differences  between  the  nervous  sys- 
tem of  man  and  that  of  the  lower  animals. 

The  elements  which  enter  into  the  nervous  substance 
require  to  be  considered  in  three  ways:  (1)  as  respects 
their  chemical  constitution ;  (2)  as  respects  their  form  or 
structure  ;  (3)  as  respects  their  general  physiological  func- 
tion. For  purposes  of  convenience  and  orderly  arrange- 
ment we  reserve  the  third  consideration  for  another 
chapter. 

CHEMISTRY  OF  THE  NERVOUS  SUBSTANCE. 

There  are  few  perfectly  certain  facts  which  can  be 
obtained  from  the  science  of  physiological  chemistry, 
respecting  the  constitution  of  nervous  matter.  These  facts 

11 


12  PHYSIOLOGICAL   PSYCHOLOGY. 

are  suggestive  and  valuable,  though  their  bearing  on  a 
theory  of  nerve-function  is  not  always  clear.  The  neces- 
sary chemical  analysis  is  encompassed  with  many  special 
difficulties.  Nervous  substance  is  a  product  of  life,  and  liv- 
ing tissue  cannot  be  at  the  same  time  preserved  in  normal 
condition  and  subjected  to  the  treatment  of  the  laboratory. 
Even  when  we  succeed  in  determining  the  constituents 
which  compose  it,  their  constitution  —  their  normal  chemical 
arrangement  and  behavior  —  cannot  easily  be  preserved. 
It  is  impossible,  for  example,  to  determine  the  specific 
gravity  of  uncoagulated  blood,  "  except  by  operating  with 
extreme  expedition,  and  at  temperatures  below  0°  C." 

Kinds  of  Nervous  Matter.  —  There  are  two  kinds  of  ner- 
vous matter, — white,  or  fibrous,  and  gray,  or  vesicular. 
These  differ  in  color,  microscopic  structure,  specific  gravity, 
and  chemical  constitution.  The  specific  gravity  of  the 
gray  matter  in  man  is  given  as  1.029-1.038;  that  of 
the  white  matter,  as  1.036-1.043.  The  lighter  weight  of 
the  gray  nervous  substance  is  due  to  the  fact  that  it 
contains  relatively  more  of  water  and  less  of  solids.  The 
percentage  of  water  and  of  solids  may  be  approximately 
given  as  follows :  of  the  gray,  81.60  and  18.40 ;  of  the 
white,  68.35  and  31.65.  The  amount  of  water  in  both 
kinds  of  nervous  substance  differs  with  age,  sex,  and  in 
different  regions  of  the  spinal  cord  and  brain.  It  is  larger 
in  the  young  animal  than  in  the  adult,  larger  in  the  brain 
than  in  the  spinal  cord.  These  facts  are  doubtless  con- 
nected with  the  degree  of  susceptibility  to  new  impres- 
sions, and  with  the  ease  with  which  changes  in  habits  are 
effected,  both  in  the  nervous  substances,  and,  as  connected 
with  it,  in  the  mind. 

Non-phosphorized  Bodies.  —  Of  the  solids  composing  the 
nervous  substance,  more  than  one-half  in  the  gray  and 
about  one-quarter  in  the  white  consist  of  certain  proteid 
or  albuminous  bodies.  Such  bodies  'are  the  only  ones 


SUBSTANCE   OF   THE   NERVOUS    SYSTEM.  13 

never  absent  from  the  active  living  cells;  they  exist  in 
all  vegetable  and  animal  organisms.  Very  little  is  known 
of  the  peculiar  chemical  constitution  which  these  proteid 
bodies  take  in  the  nerve-centres.  They  may  be  said  to 
represent  there  the  presence  of  that  general  matter  of  life 
which  is  the  physical  substratum  of  all  vital  phenomena. 

Three  other  non-phosphorized  bodies  are  found  in  the 
nervous  tissues ;  these  are  called  Cholesterin,  Neurokera- 
tin,  and,  more  doubtfully,  Cerebrin.  Cholesterin  is  abun- 
dant, especially  as  a  constituent  of  the  white  matter  of 
the  cerebro-spinal  axis  and  of  the  nerves.  It  is  supposed 
to  exist,  preformed,  in  the  brain.  It  is  described  as  a 
"  monad  alcohol,"  crystallizing  in  beautiful  white  crystals. 
Its  formula  has  been  given  as  C^H^O+HaO.  Neurokera- 
tin  may  be  derived  from  the  medullated  nerve-fibres  and 
the  gray  matter  of  the  nervous  centres;  it  is  not  found 
in  the  non-medullated  nerve-fibres.  It  contains  nitrogen 
and  a  small  percentage  of  sulphur.  Cerebrin  was  an- 
nounced by  Miiller,  in  1858,  as  a  nitrogenous  body  to  be 
obtained  from  a  precipitate  of  the  brain.  The  existence 
of  this  substance  preformed  in  the  brain  has,  however, 
been  disputed,  although  some  of  the  chemists  who  dis- 
pute its  existence  admit  the  existence  of  a  body  "for 
which  we  may  retain  the  name  of  '  cerebrin.' '  The  sig- 
nificance of  these  bodies  for  the  mental  life  is  not  appar- 
ent, except  so  far  as  the  fact  is  suggestive  that  they  are 
all  of  a  very  highly  complex  chemical  character.  Of  the 
meaning  of  this  fact  we  shall  speak  further  on. 

The  Phosphorized  Fats.  —  The  most  significant  constitu- 
ents of  the  substance  of  the  nerve-centres,  from  the  point 
of  view  both  of  chemistry  and  of  physiological  psychology, 
are  certain  complex  phosphorized  fats.  These  bodies  are 
highly  characteristic  of  the  centres  of  the  nervous  system. 
They  are  therefore  of  special  interest  to  the  student  of 
physiological  psychology.  There  are  in  particular  three 


14  PHYSIOLOGICAL  PSYCHOLOGY. 

substances  about  the  chemical  constitution  of  which  much 
dispute  has  arisen,  but  which  belong  in  this  class.  They 
are  called  Protagon,  Lecithin,  and  (more  doubtfully  again) 
Cerebrin.  Protagon  was  discovered  in  1864,  and  announced 
as  a  new  proximate  principle  that  can  be  separated  from 
the  brain,  in  a  paper  read  in  1865  (by  Dr.  Oscar  Lieb- 
reich).  Its  name  signifies  that  he  considered  it  to  "lead 
the  van."  It  is  a  very  elaborate  compound.  Its  formula 
has  been  given  as  C116H241N4O22P ;  or,  more  recently,  as 
CieoHgogNgPO^.  In  spite  of  denials  and  disputes,  subse- 
quent very  careful  researches  seem  to  make  good  the 
claim  of  protagon  to  be  the  best  established  "  phosphorized 
proximate  principle  of  the  brain."  In  calling  it  a  "proxi- 
mate principle,"  it  is  of  course  assumed  that  it  exists  pre- 
formed in  the  brain,  and  is  not  the  result  of  the  somewhat 
elaborate  process  which  is  necessary,  to  obtain  it. 

Lecithin  is  an  organic  compound  which  exists  in  large 
quantities  in  ova,  spermatozoa,  etc.,  as  well  as  in  the  ner- 
vous tissues.  It  is  supposed  by  some  to  be  only  one  of  a 
similar  group  of  bodies  which  possess  a  higher  percentage 
of  phosphorus  than  protagon,  and  is,  perhaps,  formed  from 
protagon  by  the  addition  of  the  needed  phosphorus.  We 
might  then  speak  of  "  the  lecithins "  as  a  class  of  highly 
phosphorized  compounds. 

If  we  regard  —  and  this  seems  most  probable  —  prota- 
gon as  the  definite  proximate  principle  among  the  phos- 
phorized fats  of  the  brain,  eerebrin  becomes  one  of  those 
bodies  that  are  of  ill-defined  properties,  and  doubtful  claim 
to  existence  as  proximate  principles. 

It  is  not  necessary  to  speak  in  particular  of  other  prod- 
ucts which  are  found  by  laboratory  treatment  of  the  ner- 
vous substance,  and  which  are  perhaps  to  be  regarded  as 
products  of  the  decomposition  of  protagon  and  lecithin. 

Extractive  and  Inorganic  Matters.  —  Certain  extractive 
matters,  such  as  creatin,  xanthin,  and  lactic  acids,  which 


SUBSTANCE    OF   THE   NERVOUS    SYSTEM.  15 

are  found  especially  in  the  muscles,  are  also  found  spar- 
ingly in  the  brain.  A  very  small  amount  —  varying  from 
0.1  to  1  per  cent.  —  of  inorganic  matters,  such  as  alkaline 
phosphates  and  sulphates,  chalk,  magnesia,  oxide  of  iron, 
etc.,  also  exists  in  the  brain. 

Specific  Chemistry  of  the  Elements.  —  The  more  minute 
chemistry  of  the  nerve-cells  tells  us  simply  that  they  are  in 
the  main  protoplasmic  and  therefore  rich  in  albuminous 
bodies.  Since  the  gray  matter  is  much  poorer  in  complex 
phosphorized  constituents,  we  conclude  that  the  cells, 
which  enter  into  this  matter,  are  also  poor  in  the  same 
constituents.  The  different  parts  in  the  structure  of  the 
nerve-fibres  seem  to  differ  in  chemical  constitution.  Their 
membranous  envelope,  like  that  of  the  muscles,  yields 
gelatin  on  being  boiled.  The  axis-cylinder  is  a  mixture 
of  albuminous  and  complex  fat-like  bodies.  The  chemical 
constitution  of  the  nervous  elements  of  the  retina  of  the 
eye  is  very  closely  related  to  the  phenomena  of  sight ; 
for  this  sense  is  thought  to  be  dependent  upon  the  pro- 
duction, by  the  stimulus,  of  photo-chemical  changes  in 
these  elements.  The  retina  seems,  accordingly,  to  contain 
the  same  bodies  as  the  central  nervous  system.  Even  the 
two  segments  into  which  the  rods  and  cones  of  the  retina 
break  up  exhibit  marked  differences  in  their  chemical,  as 
well  as  optical  characteristics. 

Chemistry  of  the  Functions  of  the  Nerve-Elements.  —  Like 
every  other  natural  material  structure,  the  nervous  system 
is  obviously  adapted  to  a  peculiar  kind  of  work.  Chem- 
ically considered,  it  has  two  very  important  characteris- 
tics :  its  constitution  is  extremely  complex,  and  the 
compounds  that  enter  into  it  are  highly  unstable.  It  is 
evident,  then,  that  it  contains,  stored,  a  large  amount  of 
disposable  energy ;  and,  also,  that  it  readily  yields  Ms 
energy,  whenever  the  equilibrium  of  its  molecules  is  even 
slightly  disturbed.  But  a  more  remarkable  thing  about 


16  PHYSIOLOGICAL   PSYCHOLOGY. 

it  is,  that  —  as  we  shall  see  later  on  —  it  explodes,  as  it 
were,  with  increasing  surrender  of  its  energy  as  the  num- 
ber and  intensity  of  the  demands  upon  it  are  increased. 
Within  certain  limits,  it  behaves  very  much  as  would  a 
convenient  kind  of  gun,  which  should  be  so  arranged  as 
to  go  off  with  greater  energy,  as  the  pressure  of  one's 
finger  on  the  trigger  were  repeated  or  increased. 

More  wonderful  still,  —  the  nervous  substance  may  be 
said  to  make  its  own  powder  as  fast  (within  certain  limits) 
as  it  is  burned.  It  is  itself  the  seat  of  a  chemical  synthe- 
sis, which  results  in  constructing  the  peculiar  bodies  just 
described,  from  the  material  furnished  by  the  blood. 
Such  bodies  have  a  high  value  as  combustibles ;  for  —  as 
has  been  said  —  they  hold  in  store  a  large  amount  of 
easily  disposable  energy.  Yet  further,  the  nerves,  as 
distinguished  from  the  nerve-centres  and  the  end-organs 
of  sense,  can  act  repeatedly  in  quick  succession  with 
undiminished  force.  It  would  seem,  then,  that  they  must 
have  the  power  of  recombining  immediately  the  molecules 
which  have  been  thrown  down  from  their  condition  of  a 
highly  complex  compound  having  an  unstable  equilibrium. 
Nerves  appear  to  be  so  constituted  chemically,  that  they  can 
serve  as  laboratories  to  retain  the  constituents  of  their  own 
substance  and  to  reform  them  as  fast  as  they  are  dissolved. 

It  is  therefore  impossible  not  to  regard  the  substance 
of  the  nervous  system  as  especially  fitted  by  its  chemical 
constitution  to  serve  the  purpose  which  it  actually  per- 
forms. It  is  so  constituted  as  to  be  in  a  high  degree 
susceptible  to  the  slightest  attacks  from  various  kinds  of 
stimuli.  It  acts  and  recovers,  and  propagates  the  changes 
set  up  in  any  part  of  it,  with  a  high  degree  of  rapidity. 
It  stores  in  compact  form  a  large  amount  of  easily  dis- 
posable energy.  It  is  precisely  such  a  system  of  physical 
bodies  as  this,  which  is  fitted  to  be  especially  correlated 
with  the  phenomena  of  conscious  sensation  and  motion. 


SUBSTANCE   OF   THE    NERVOUS    SYSTEM.  17 


STRUCTURE  OF  THE  NERVOUS  ELEMENTS. 

From  the  science  of  chemistry  we  now  turn  to  the 
science  of  microscopic  anatomy  or  histology,  and  inquire 
what  it  can  tell  us  with  respect  to  the  structural  form  of 
the  nervous  elements.  If  we  analyze  with  a  microscope 
a  section  of  the  nervous  matter  of  the  central  organs,  its 
apparently  homogeneous  character  breaks  up  into  three 
or  four  kinds  of  substances.  Of  these  one  at  least  is  not 
generally  considered  to  have  a  nervous  character. 

Neuroglia.  —  A  diffuse,  finely  granular  substance,  called 
'neuroglia  "  or  "  nerve-cement  "  exists  in  quantities  large 
enough  to  form  an  essential  part  of  some  localities  of  the 
brain  and  spinal  cord.  It  appears  on  examination  to  be 
a  delicate  net-work,  in  which  certain  small  cells  (called 
"  neuroglia  cells  "),  supposed  to  belong  to  the  sus tentac- 
ular tissue,  and  other  more  conspicuous  cells,  usually  of  a 
stellate  shape,  are  found.  It  is  not  always  clear  to  what 
its  appearance  of  granular  or  molecular  matter  "is  due. 
The  office  of  the  neuroglia  is  supposed  to  be  —  as  the 
name  signifies  —  the  holding  in  place  of  the  true  nerve- 
elements  by  filling  in  the  gaps  between  them.  It  is 
therefore  classed  with  the  connective,  or  sustentacular, 
rather  than  the  nervous  tissue ;  although  it  forms  a  con- 
stituent of  the  nervous  substance  in  the  great  nerve- 
centres. 

Nerve-corpuscles.  —  Very  minute  bodies,  scarcely  more 
than  from  ^rV^  to  -5^-$  of  an  inch  in  diameter,  and  con- 
sisting either  of  naked  nuclei  or  of  nuclei  with  only  a 
small  amount  of  surrounding  protoplasm,  are  found  abun- 
dantly in  the  gray  matter  of  certain  of  the  nervous  centres. 
Some  of  them,  like  the  typical  nerve-cells,  give  off  proc- 
esses. They  vary  much  in  shape,  —  are  multipolar, 
bipolar,  or  unipolar.  Some  of  them  so  closely  resemble 
the  more  highly  developed  nerve-cells  called  "  ganglionic  " 


18  PHYSIOLOGICAL   PSYCHOLOGY. 

that  they  have  been  described  as  "  nuclei  invested  by  only 
a  small  quantity  of  cell-substance."  It  is  probably  not 
possible  to  draw  any  fixed  line  through  this  class  of 
minute  bodies,  or  to  separate  the  more  highly  developed 
members  of  the  class  from  the  larger  and  more  elaborate 
bodies  to  which  the  name  of  "  nerve-cells "  is  unhesi- 
tatingly given.  They  may  therefore  be  regarded  as  nerve- 
corpuscles  in  various  stages  of  development,  from  mere 
granules  to  ganglionic  cells. 

The  undoubtedly  nervous  elements  of  the  substance  of 
the  nervous  system  are  of  two  kinds,  as  respects  their 
structural  form:  these  are  nerve-fibres  and  nerve-cells. 
The  white  matter  of  the  peripheral  nerves  and  of  the 
nerve-centres  is  composed  of  nerve-fibres.  The  gray  mat- 
ter of  the  nerve-centres  contains,  besides  the  nerve-fibres, 
numerous  nerve-cells.  Both  these  elements  require  then 
a  more  detailed  description. 

NERVES,  NERVE-FIBRES  AND   THEIR  FIBRILS. 

Nerves.  —  What  is  ordinarily  called  a  "  nerve  "  appears 
to  the  naked  eye  as  a  cord  of  a  whitish  or  grayish  color 
and  uniform  structure.  On  examination,  however,  we 
find  that  it  consists  of  several  bundles  (or  "fascicles  "),  of 
various  seizes,  bound  together  by  connective  tissue.  When 
followed  toward  the  surface  of  the  body,  it  divides  and 
subdivides,  until  its  subdivisions  consist  of  a  single  nervous 
element  called  a  nerve-fibre.  The  bundles  of  the  nerve  are 
enclosed  in  a  special  sheath  (called  neurilemma  or  peri- 
neurium).  As  the  nerve-fibres  run  toward  the  central 
organs  they  are,  as  has  been  indicated,  bound  together  to 
form  a  nerve-fascicle.  J^  small  amount  of  connective  tissue 
appears  between  the  several  fibres  within  the  same  sheath. 
The  character  of  the  sheath  itself  is  changed  and  it 
becomes  attached  to  surrounding  structures  by  a  layer  of 
connective  tissue. 


SUBSTANCE   OF   THE   NERVOUS    SYSTEM. 


19 


Kinds  of  Nerve-fibres.  —  The  nerve-fibres  which  compose 
those  nerves  that  run  from  the  central  organs  to  the  pe- 
ripheral parts  of  vertebrate  animals,  are  divided  into  two 
classes.  These  are  called  medullated  nerve-fibres,  or  nerve- 
tubes,  and  non-medullated  nerve-fibres,  or  fibres  of  Remak. 


n 


FIG.  1.  — Cross-section  of  the  Sciatic  Nerve  of  Man.  8A.  (After  Key  and  Retzius.) 
The  left  lower  half  is  schematic,  n,  n,  Bundles  of  nerve-fibres,  surrounded  by  pn,  pn, 
the  perineurium  :  between  them  appears  the  connective  tissue,  epineurium  (ep,  ep),  and 
adipose  substance  (ad). 

The  former  belong  particularly  to  the  brain  and  spinal 
cord;  they  are  found  only  in  vertebrate  animals.  The 
latter  belong  particularly  to  the  sympathetic  system.  This 
distinction,  which  is  easy  to  make  for  the  peripheral  nerves, 
becomes  difficult  or  impossible  when  we  attempt  to  carry 
it  out  within  the  more  complex  nerve-matter  of  the  central 
organs. 

Within  the  nerve-centres  of  the  brain  and  spinal  cord 
there  appears,  at  first  sight,  to  be  a  considerable  variety  of 
nerve-fibres.  Here  we  find  very  fine  nerve-threads  which 


20 


PHYSIOLOGICAL   PSYCHOLOGY. 


require  an  enlargement  of  five  hundred  or  more  diameters 
to  make  them  even  visible.  Certain  very  delicate  trans- 
parent lines,  differing  from  the  fore- 
going by  their  larger  size  and  fibrillar 
structure,  also  appear.  These  are 
the  so-called  "  naked  axis-cylinders." 
Both  of  these  may  be  invested  with 
a  medullary  sheath  and  so  converted 
into  medullated  nerve-fibres.  Or,  in 
the  peripheral  nerves,  they  may  be 
found  without  such  a  sheath.  And 
whether  medullated  or  not,  they  may 
become  invested  with  a  delicate  cov- 
ering membrane  (called  "  sheath  of 
Schwann"). 

It  will  be  noticed,  however,  that  it 
is    the    presence    or    absence    of    the 
medullary    sheath   which    constitutes 
the  one  important  difference  between 
the   different   classes  of   nerve-fibres. 
It  is   therefore   customary   to    distin- 
guish only  two  kinds  of  nerve-fibres, 
according  as  they  have,  or  have  not, 
this  covering  of  medullary  substance. 
Fibres    of    Remak.  —  These    nerve- 
fibres  are  distinguished  chiefly  by  the 
absence    of    the    medullary    sheath. 
They   are    grayish    and    translucent, 
with  flattened  nuclei  lying  at  frequent 
no.  2.  -Fibres  of  Remak  intervals  along  their  surface.     When 
gathered    into    bundles,    within    the 
j;  sheath   of   neurilemma,  they  are   not 
ing  to'f!bri1^  placed  side  by  side.     They  are  rather, 

as  it  were,  formed  within  the  interior  of  the  nerve,  where 
they  unite  and  divide  so  as  to  form  an  intricate  net-work 


SUBSTANCE    OF   THE   NERVOUS    SYSTEM. 


21 


of  fibres.  When  grouped  into  still  larger  bundles,  or 
nerves,  they  are  sometimes  alone,  but  are  more  frequently 
connected  with  the  medullated  fibres. 

Medullated  Nerve-fibres.  —  By  carefully  teasing  a  nerve 
with  fine  needles  we  may  separate  its  fibres  for  micro- 
scopic examination.  While  still  fresh,  certain  of  the  fibres 
appear  with  a  central  part  and  a  border 
on  each  side,  like  a  translucent  liquid 
in  a  tube  of  translucent  walls. 

By  using  different  staining  solutions, 
which  act  differently  upon  the  different 
parts  of  its  structure,  the  three-fold 
character  of  the  medullated  nerve-fibre 
is  demonstrated.  We  thus  distinguish  : 
(1)  An  outer  membrane,  extremely  thin, 
pellucid,  and  having  nuclei,  called  the 
"sheath  of  Schwann";  (2)  an  interior 
layer  of  dimly  granular,  white,  and  highly 
refracting  substance,  semi-liquid  during 
life,  and  called  the  "  medullary  sheath  "  ; 
and  (3)  a  cylindrical  band  of  transparent 
albuminous  material,  called  the  "axis- 
cylinder." 

Since  many  nerve-fibres,  although  they  Bbowing-  ~(Schwalbe-> 
are  only  naked  axis-cylinders,  perform  truly  nervous  func- 
tions, we  conclude  that  this  interior  portion  of  the  nerve- 
tube  is  alone  essential  to  its  nervous  character.  The 
sheaths  may  then  be  regarded  as  insulators. 

Besides  its  three-fold  longitudinal  character,  modifi- 
cations in  the  structure  of  the  nerve-fibre  occur  along  its 
length.  Of  these,  two  are  most  important.  Places  of 
constriction  appear  at  certain  points,  situated  beneath  the 
outer  sheath ;  these  constrictions  are  made  at  the  expense 
of  the  medullary  sheath.  They  are  called  annular  con- 
strictions, or  nodes  of  Ranvier.  The  portion  of  the  nerve- 


FIG.  3.  —  Medullated 
Nerve-fibres,with  double 
and  irregular  contour 


OrH 


B 


7t-~{ 


FIG.  4.  —  A,  Medullated  Nerve-fibres  from 
the  Sciatic  of  a  Rabbit,  Btained  with  psmic 
acid,  and  dissociated  in  water.  (Ranvier.) 

B,  Single  Fibre  Enlarged  40%.  a,  a,  An- 
nular constrictions,  or  nodes  of  Ranvier, 
nearly  midway  between  which  is  11,  the 
nucleus,  with  protoplasm, p,  surrounding  it; 
ca,  axis-cylinder. 


71 


FIG.  5.— Medullated  Nerve  -  fibres. 
(Schwalbe.)  a,  Axis-cylinder;  s,  sheath 
of  Schwann;  n,  nucleus;  p,  p,  granular 
substance  at  the  poles  of  the  nucleus; 
r,  r,  Ranvier's  nodes,  where  the  me- 
dullary sheath  is  interrupted  and  the 
axis-cylinder  appears;  it  i,  incisures  of 
Schmidt. 


SUBSTANCE   OF  THE  NERVOUS   SYSTEM. 


23 


fibre  included  between  two  of  them  is  called  an  "inter- 
annular  segment." 

Each  segment  of  a  nerve-fibre  has  a  flattened  elliptical 
nucleus,  generally  about  half-way  between  the  two  nodes 
which  bound  the  segment.  This  nucleus  sometimes  com- 
prises within  it  a  still  smaller  nucleus  (nucleolus).  Be- 
tween the  nucleus  and  the  medullary 
substance  there  exists  a  minute  mass  of 
protoplasm. 

Other  small  irregularities  of  structure, 
which  the  medullated  nerve-tubes  exhibit 
under  the  higher  powers  of  the  micro- 
scope, it  is  not  necessary  to  describe  (see, 
however,  Fig.  5). 

Fibrils  of  the  Axis-cylinder,  —  A  discus- 
sion has  been  going  on  for  some  forty  or 
fifty  years  as  to  the  meaning  of  certain 
yet  more  minute  divisions  which  appear, 
under  the  very  highest  powers  of  the 
microscope,  in  the  structure  of  the  axis- 
cylinder  of  medullated  nerve-fibres.  Some 
investigators  claim  that  fibrils  can  be  dis- 
tinctly traced  (as  see  Fig.  6)  in  living 
nerve-fibres,  where  they  are  in  process 
of  forming  and  are  still  naked,  or  where 
they  are  seen  just  issuing  from  nerve-cells. 
These  fibrils  they  regard  as  the  ultimate 
"  nerve-lines  "  —  swimming  or  suspended, 
as  it  were,  in  a  semi-fluid  medium  —  along 
which  the  nerve-processes  run.  But  others  regard  the 
substance,  in  which  these  "primitive"  fibrils  appear  sus- 
pended, as  the  real  nervous  substance ;  and  they  describe 
it  as  diffused  in  the  cavities  of  a  sponge-like  network. 

Whichever  of  the  foregoing  views  is  taken,  it  would 
seem  that  the  structure  of  even  the  axis-cylinder  is  not 


24  PHYSIOLOGICAL   PSYCHOLOGY. 

homogeneous ;  but  that  it  contains  provision  for  parallel 
or  interlacing  lines  of  nerve-action,  running  along  within 
the  delicate  covering  of  cells  which  forms  its  limit.  So 
marvellously  minute  and  complicated  are  even  the  so-called 
elements  of  this  nervous  mechanism ! 

Size  of  Nerve-fibres.  —  As  a  rule,  the  non-medullated 
nerve-fibres  are  smaller  than  the  medullated,  —  the  former 
being  from  ^V*r  to  -g-^  of  an  inch  in  diameter,  and  the  lat- 
ter from  y^nj-  to  ^innr-  But  this  rule  is  not  always  followed. 
In  the  white  matter  of  the  spinal  cord  the  medullated 
fibres  vary  in  size  from  y^nr  to  ^oW  °f  an  incn  5  but  near 
the  gray  matter  of  the  cord,  they  are  sometimes  not  more 
than  y^j-g-  of  an  inch.  The  fibres  are  much  finer  in  the 
gray  matter  of  the  cord  and  brain  (7-^  to  YT  Jinr  of  an  inch 
in  diameter) ;  they  are  finest  of  all  in  the  superficial  layers 
of  the  brain,  or  in  the  nerves  of  special  sense.  In  some 
instances  the  axis-cylinder  may  be  not  more  than  Yinnnnr  °f 
an  inch  in  diameter. 

GANGLIONIC  NERVE-CELLS. 

The  undoubtedly  nervous  cells  vary  greatly  in  size  and 
shape,  but  when  subjected  to  the  microscope  they  all  ex- 
hibit certain  common  characteristics. 

Ganglion-cells.  —  These  nerve-corpuscles  may  be  de- 
scribed as  irregular  masses  of  protoplasm,  finely  granular 
and  delicately  striated,  with  a  large  nucleus  which  is  well 
defined  and  vesicular  in  appearance,  and  usually  contains  a 
shining  nucleolus.  They  send  off  one  or  more  processes. 
In  shape,  some  are  nearly^  round ;  others  are  egg-shaped, 
Caudate,  stellate,  or  like  a  flask  or  the  blade  of  a  paddle ; 
still  others  resemble  the  foot  of  an  animal  with  claws.  In 
size  they  vary  from  about  ^  to  -g^Vff  of  an  inch. 

To  a  certain  extent,  the  shape  and  size  of  the  nerve-cells 
are  characteristic  of  the  part  of  the  central  nervous  system 
where  they  are  found.  For  example,  large  cells  of  irreg- 


SUBSTANCE   OF  THE   NERVOUS   SYSTEM. 


25 


ular  shape  with  branching  processes  are  found  in  the 
"  motor  "  regions  of  the  spinal  cord.  Cells  very  similar  to 
these  seem  also  to  be  present  in  certain  "  motor  "  regions 
of  the  brain.  Pyramidal  cells  are  char- 
acteristic of  the  cortex,  or  gray  rind,U- 
of  the  brain ;  and  a  peculiar  layer  of 
irregular  globular  cells  is  found  just  at 
the  inner  edge  of  the  gray  matter  of 
the  cerebellum.  The  most  recent  re- 
searches indicate  the  possibility  of  dis- 
tinguishing the  sensory  from  the  motor 
cells  in  the  cortex  of  the  brain.  The 
former  are  thought  by  some  observers  to 
be  smaller  in  size,  flask-shaped  or  bal- 
loon-shaped, and  less  susceptible  to 
staining.  In  the  same  regions  the 
motor  type  is  thought  to  be  pyramidal. 
The  Ganglionic  Globe.  —  The  higher 
powers  of  the  microscope  reveal  the 
bewildering  complexity  of  the  structure 
of  the  fully  developed  nerve-cell.  But 
regarding  its  details  there  is  still  uncer- 
tainty and  dispute.  The  bipolar  gan- 
glion-cell of  the  fish  has  usually  been 
considered  as  a  common  type.  This  cell 
has  two  parts :  (1)  A  covering,  which  is 
described  as  "  fibrillary " ;  and  (2)  a 

.    -  i        p  i  ijj  FIG.  7.— Nerve-cell  from 

globe  composed  or  granular  substance    the  spinal  Ganglion  of  the 

j  ,     .     .  .,  £  Ray.  35%-  (Ranvier.)  my, 

and    Containing    near    itS    SUriaCC     a    nU-     Medullary  sheath  of  nerve- 

,       , .  fibre,    enclosing    ca,    the 

cleUS    With    One     Or    more     nUCleoll.        A     axis-cylinder,    the    fibrils 

.of  which  (/)  separate  and 

recent  description   from   this   point  of   «m  over  the  gangiionic 

x  .  globe,  m',  n,  nucleus. 

view  makes  the  nerve-cell  consist,  not 
only  of  a  nucleus,  but  also  of  a  "  dense  tangle "  of  ex- 
tremely minute  fibrils  with  an  irregularly  granular  material 
filling  the  spaces  between  them. 


26  PHYSIOLOGICAL  PSYCHOLOGY. 

Others  regard  the  "  fibrillary  "  or  "  striated  "  appearance 
of  the  cell  as  indicating  that  the  exceedingly  small  ("  primi- 
tive ")  nerve-tubules,  of  which  it  mainly  consists,  are  sus- 
pended, as  it  were,  in  a  spongy  network  within  the  cell- 
body. 

Processes  of  the  Ganglion-cells.  —  It  is  generally  agreed 
that  two  kinds  of  processes  are  given  out  by  certain  of  the 
nerve-cells ;  but  the  character  and  fate  of  these  processes 
are  still  in  dispute.  Deiters  and  others  describe  the  case 
—  and  their  account  has  until  recently  been  the  accepted 
one  —  in  the  following  way :  Ordinarily,  only  one  of  the 
processes  of  the  nerve-cell  becomes  continuous  with  the 
axis-cylinder  of  a  nerve-fibre.  This  process  is  therefore 
called  the  "axis-cylinder  process."  It  can  often  be  dis- 
tinctly seen  to  be  fibrillated ;  its  fibrils  are  continuous  with 
those  of  the  axis-cylinder  of  the  nerve-fibre.  The  other 
processes,  also,  have  fibrils,  but  they  are  not  continuous 
with  those  of  any  nerve-fibre.  These  latter  processes  are 
sometimes  called  "  branching,"  since  their  fibrils  ramify, 
separate,  and  unite  again,  and  finally  become  lost  in  an 
intricate  network  of  extremely  minute  nervous  filaments. 

Others,  whose  investigations  are  more  recent  (Golgi, 
Forel,  Kolliker),  maintain  that  the  axis-cylinder  process 
is  always  found  to  be  branched.  In  some  cases  the  axis- 
cylinder  maintains  its  identity,  but  gives  off  many  fine 
lateral  branches.  In  others,  the  branching  is  more  profuse 
and  rapid,  and  the  axis-cylinder  soon  loses  its  identity. 
These  investigators  also  deny  that  the  so-called  "  branch- 
ing processes,"  which  do  not  become  continuous  with  axis- 
cylinders,  communicate  with  each  other;  they  do  not 
"  anastomose." 

CONNECTION  OF  THE  NERVE-FIBRES  AND  NERVE-CELLS. 

Few  subjects  of  microscopic  anatomy  are  more  baffling, 
and  at  the  same  time  more  interesting  and  important,  than 


SUBSTANCE  OF   THE  NEKVOUS   SYSTEM.  27 

the  exact  determination  of  the  physical  connection  between 
the  two  principal  elements  of  the  nervous  substance. 
On  the  one  hand,  it  has  been  held  that  no  connection 
between  nerve-cells  and  nerve-fibres  can  ever  certainly  be 
made  out,  and  that  even  its  existence  is  doubtful  (e.g.  by 
Wyman,  in  1852).  Next,  a  direct  connection  is  thought  to 
be  made  out  in  certain  instances  and  assumed  to  hold  good 
as  a  rule  (e.g.  by  Vulpian,  in  1866).  Then  we  have  the  defi- 
nite theory,  said  to  be  "  established,"  that  for  every  nerve- 
cell  there  is  a  corresponding  nerve-fibre  which  is  continuous 
with  its  one  "  axis-cylinder  process."  Thus  the  ganglionic 
nerve-cell  is  assumed  to  be  "the  one  perfectly  definite  type  " 
of  all  the  seemingly  different  nerve-elements.  .  Nerve-fibres 
are,  accordingly,  described  as  nerve-cells  drawn  out  into  a 
long  process  which  serves  to  connect  them  with  other  sim- 
ilar cells  and  fibres,  or  perhaps  with  the  muscular  fibres 
which  the  nervous  substance  commands.  On  the  other 
hand,  the  more  careful  recent  researches  seem  to  indicate 
that  the  relations  between  the  separate  elements  of  the 
nervous  substance  are  much  more  intricate  and  often  indi- 
rect than  this  captivating  theory  would  lead  us  to  suppose. 
In  the  midst  of  such  contradictory  evidence  from  the 
experts  themselves,  we  may  content  ourselves  with  stating 
the  views  of  the  more  recent  investigators.  For  in  the 
use  of  the  higher  powers  of  the  microscope  only  what  is 
recent  is  of  much  value.  The  more  recent  views  main- 
tain that  rarely,  if  ever,  does  a  direct  origin  of  the  nerve- 
tubes  from  the  nerve-cells  take  place.  The  slender  fibrils 
of  the  central  nervous  substance  come,  partly,  from  the 
breaking  up  of  the  processes  of  the  nerve-cells ;  they 
come  also,  partly,  from  nerve-tubes  that  run  across  from 
one  portion  of  this  substance  to  another,  or  run  into  it 
from  the  periphery  of  the  nervous  system.  It  is  in  this 
"  fibrillar  mass,"  which  must  be  regarded  as  interposed 
between  them  and  the  nerve-cells,  that  the  nerve-tubes 


28  PHYSIOLOGICAL   PSYCHOLOGY. 

have  their  origin.  In  other  words,  the  connection  between 
nerve-cells  and  nerve-fibres  of  the  peripheral  nerves  is  ordi- 
narily indirect. 

The  attempt  has  been  made  to  procure  additional  evi- 
dence on  this  subject  by  counting  the  nervous  elements 
of  both  kinds  in  the  ganglia  and  roots  of  the  same  sections 
of  the  spinal  cord.  But  this  method  gives  conflicting 
results.  One  investigator  (E.  A.  Birge)  finds  that  his 
count  makes  the  number  of  fibres  and  cells  so  nearly  alike 
(e.g.  in  ten  motor  roots  5734  fibres  and  5777  cells)  as 
to  give  countenance  to  the  theory,  that  each  fibre  has  a 
-special  direct  connection  with  a  single  cell.  Other  inves- 
tigators, however,  find  their  count  favoring  the  view  that, 
in  the  roots  of  the  spinal  cord,  two  cells,  as  a  rule,  unite 
their  processes  to  make  up  the  axis-cylinder  of  a  single 
nerve-fibre.  Some  observers  claim  to  have  seen  through 
the  microscope  cases  of  such  a  union. 

It  must  be  admitted,  therefore,  that  the  exact  manner 
of  the  connection  between  the  nerve-cells  and  the  nerve- 
fibres  is  not,  as  yet,  determined.  The  evidence  goes  to 
show,  however,  that  it  is  very  largely  indirect.  But 
possibly  both  kinds  of  connection — -namely,  the  direct 
and  the  indirect  —  may  be  at  some  time  established  to  the 
satisfaction  of  all  parties.  It  may  then,  also,  be  possible 
to  tell  what  is  the  meaning,  as  respects  the  function  of 
the  nervous  elements,  of  these  two  kinds  of  connection. 
And,  indeed,  some  very  careful  observers  have  already 
advanced  the  theory,  that  the  connection  is  direct  in  the 
case  of  the  motor  nerve-tubes,  and  indirect  in  the  case  of 
the  sensory  nerve-tubes.  But  this  theory  has  at  present 
no  sufficient  evidence. 


SUBSTANCE   OF   THE   NEKVOUS   SYSTEM.  29 


CONCLUSIONS    FROM     THE    STRUCTURE     OF     THE    NERVE- 
ELEMENTS. 

In  spite  of  all  doubts  respecting  many  and  important 
details  of  the  structural  character  of  the  nervous  sub- 
stance, the  general  bearing  of  what  is  known  is  evident 
enough.  The  entire  nervous  system  of  man  is  compounded 
of  a  very  few  kinds  of  nerve-elements,  put  together  into 
a  great  variety  of  organs,  whose  structure  and  functions 
the  subsequent  chapters  will  explain.  Here  then  is  a 
wonderful  unity  composed  of  an  almost  infinite  complex- 
ity. The  nerve-elements  are  essentially  the  same  in  all 
the  organs  of  man's  nervous  system.  The  same  kind  of 
molecular  disturbance,  called  "  nerve-commotion  "  or  ner- 
vous "impulse,"  may  be  supposed  to  be  producible  and 
capable  of  propagation  in  them  all.  But  even  these 
elements  are  so  indescribably  fine  in  their  structure,  and 
are  probably  connected  to  form  the  system  in  such  an 
infinite  number  of  slightly  different  ways,  that  this  nerve- 
commotion  can  be  indefinitely  varied  as  to  its  shading, 
intensity,  and  extent  and  paths  of  distribution. 

Especially  do  we  notice  that  the  elements  of  the  ner- 
vous system  are  fitted  to  form  "  tracts  "  along  which  the 
nerve-commotion  may  run.  Every  nerve-fibre  constitutes 
one  such  tract,  —  capable,  it  would  seem,  of  subdividing 
at  either  end  into  a  considerable  number  of  fibrils  or  sub- 
ordinate tracts.  The  nerve-cells,  too,  seem  fitted  to  serve 
as  tracts  for  the  propagation,  and  perhaps  also  as  centres 
for  the  distribution  and  modification  ("  shunting  places  " 
they  have  sometimes  been  called)  of  the  same  nerve- 
commotion.  The  processes  which  they  give  off  —  whether 
directly  or  only  indirectly,  or  both,  does  not  concern  our 
present  purpose  to  determine  — serve  to  bring  them  into 
connection  with  other  nerve-elements  of  the  same  kind; 
and  through  the  peripheral  nerves,  with  the  muscles  and 


x .; 

30  PHYSIOLOGICAL   PSYCHOLOGY. 

special  organs  of  sense.  Both  kinds  of  nerve-elements 
are  certainly  adapted  to  serve  the  purpose  of  "  conduc- 
tivity "  in  an  exceedingly  complex  system  of  interrelated 
organs. 

Among  the  organs  of  the  nervous  system,  moreover, 
we  shall  find  prominent  the  so-called  "end-organs  of 
sense."  Of  course,  the  importance  of  these  organs  for 
the  life  of  the  mind  needs  no  defence.  But  the  organs 
of  sense,  in  so  far  as  they  are  nervous  in  character  and  so 
capable  of  serving  the  purposes  of  a  life  of  conscious  sen- 
sation, are  constructed  by  combining  the  same  two  nerve- 
elements, — namely,  the  nerve-fibres  and  the  modified  nerve- 
cells.  The  "  irritability  "  of  the  nerve-elements  is  therefore 
an  indispensable  thing.  As  a  matter  of  function,  it  is 
provided  for  in  their  very  structure.  They  are  so  made, 
so  delicate  and  so  sensitive,  that  the  slightest  amount  of 
the  appropriate  kind  of  stimulus,  furnished  by  external 
nature,  stirs  them  to  nervous  action. 

In  a  still  more  wonderful  manner  do  we  find  that  these 
elements,  when  combined  into  the  central  organs  of  the 
brain,  are  irritable  in  correlation  with  all  the  changing 
phases  of  the  mind.  For  this  reason,  among  others,  we 
may  be  inclined  to  maintain,  that  no  other  mechanism  in 
nature  is  so  surprisingly  fitted  for  the  most  important 
relations  as  that  which  is  made  by  combining  the  nervous 
elements.  As  a  system,  this  mechanism  depends,  for  what 
it  is  and  for  what  it  can  do,  upon  the  structure,  chemical 
and  microscopic,  of  the  nerve-corpuscles  and  nerve-fibres  of 
which  it  is  composed. 


CHAPTER  II. 

STRUCTURE   OF  THE  SPINAL   CORD  AND  BRAIN. 

THE  nervous  elements,  whose  chemical  constitution  and 
formal  structure  were  described  in  the  last  chapter,  are 
combined  into  a  great  variety  of  "  organs ";  and  these 
organs  are  systematically  arranged,  in  relation  to  each 
other,  for  the  accomplishment  of  a  common  work.  This 
arrangement  of  organs,  all  of  which  are  made  by  com- 
bining the  nerve-fibres  and  nerve-corpuscles  in  their  "  bed- 
ding" of  connective  tissue,  is  called  —  significantly — the 
"  Nervous  System."  It  is  the  mutual  condition  and  recip- 
rocal action  of  the  elements  which  give  its  peculiarities 
to  this  mechanism. 

It  will  greatly  assist  our  understanding  of  the  nervous 
system  if  we,  from  the  first,  regard  it  in  the  light  of  an 
appropriate  idea.  Such  an  idea  is  secured  when  we  con- 
sider the  whole  as  a  natural  development  in  response,  as  it 
were,  to  a  problem  requiring  a  mechanical  solution.  This 
idea  may  be  presented  more  clearly  by  considering  how  a 
similar  but  much  simpler  problem  is  solved  by  an  amoeba. 
The  amoeba,  under  the  microscope,  appears  wholly,  or 
almost  wholly,  structureless.  But  it  is,  of  course,  com- 
posed of  a  great  number  of  molecular  elements  which  are 
undergoing  constant  change.  It  is  alive  ;  its  substance  is 
therefore  (1)  metabolic,  (2)  respiratory,  (3)  reproductive. 
But  more  important  still  for  our  purpose  is  the  fact  that 
the  amoeba  is  (4)  irritable  and  (5)  automatic.  When  it  is 
acted  on  by  stimuli  from  without,  it  suffers  an  explosion  of 
energy  which  generally  results  in  its  changing  its  form  and 

31 


32  PHYSIOLOGICAL  PSYCHOLOGY. 

place.  Some  of  its  movements  seem  rather  due  to  unknown 
internal  changes,  and  are  therefore  called  "automatic." 
Thus  does  the  amoeba  solve  its  problem  of  adjusting  itself 
to  its  changing  environment. 

Let  now  the  problem  become  much  more  complicated, 
and  the  mechanism  employed  for  its  solution  correspond- 
ingly complex.  The  metabolic,  respiratory,  and  repro- 
ductive functions  of  the  animal  will  each  have  separate 
systems  of  organs  assigned  to  their  use.  A  system  of 
muscles  will  be  formed  which  will  possess  in  an  eminent 
degree  the  "  amoeboid  contractility."  But  the  property  of 
being  irritable  and  automatic  will  become  the  special  endow- 
ment of  the  nervous  system. 

A  greater  differentiation  of  organs  and  functions  of 
organs  must  take  place  as  the  problem  of  the  life  of  the 
animal  becomes  more  complex.  Certain  groups  of  cells 
must  become  more  eminently  irritable  or  susceptible  to 
external  stimuli ;  certain  others  more  eminently  automatic 
or  susceptible  to  internal 'stimuli.  But  if  all  the  groups  of 
cells  are  to  be  connected  into  one  system,  strands  of  irritable 
protoplasm  must  be  stretched  between  them,  —  thus  binding 
them  together  into  a  community  of  action.  Still  further : 
it  is  obviously  necessary  that  the  muscular  system,  upon 
which  the  separate  movement  of  the  different  masses  of  the 
animal's  body,  or  of  its  whole  body  at  once,  depends,  shall 
be  connected  with  both  the  external  and  the  internal  groups 
of  cells.  Only  in  this  way  can  the  various  forces  of  nature 
reflexly  influence  its  movements,  designed  —  as  they  are 
—  to  keep  it  adjusted  to  its  changing  environment;  only 
in  this  way  also  can  the  animal  exercise  any  "  will  of  its 
own." 

The  most  highly  developed  nervous  system  will,  then, 
consist  of  the  following  necessary  parts :  (A)  End-organs 
of  Sense,  like  the  skin,  the  eye,  the  ear,  etc. ;  (^')  End- 
organs  of  Motion,  like  the  attachments  which  the  nerves 


STRUCTURE   OF   THE   SPINAL   CORD   AND   BRAIN.        33 

have  to  the  muscles ;  (-S)  Central  Organs,  like  the  periph- 
eral ganglia,  the  spinal  cord  and  the  brain,  —  in  which  may 
come  to  exist  (5)  certain  regions  more  distinctively  motor, 
and  (6')  others  more  distinctively  sensory,  and  (b!f)  perhaps 
still  others  more  particularly  intellectual ;  and  finally,  ( (7) 
Conducting  Nerves,  which  will  be  either  (c)  afferent  and 
sensory,  or  (V)  efferent  and  motor. 

Now  the  nerve-elements  in  man  are  actually  combined 
into  these  various  classes  of  organs  —  namely,  end-organs 
of  sense  and  motion,  central  organs,  and  conducting  , 
nerves  —  to  make  a  nervous  system.  To  accomplish  this, 
the  nerve-fibres  are  bound  into  bundles,  called  "nerves," 
in  the  manner  already  described  (p.  18).  The  nerve-cells 
are  grouped  into  masses  of  nervous  matter,  called  ganglia,  . 
or  gathered  into  larger  bodies ;  and  these  are  intersected 
with  minute  ramifications  of  the  nerves,  and  interspersed 
with  the  finely  granular  substance  called  neuroglia.  Of 
these  masses  or  larger  bodies,  together  with  the  nerve- 
cords  which  connect  them,  two  so-called  systems  are 
formed.  These  are  called  the  "  Sympathetic  System  "  and 
the  "  Cerebro-spinal  System." 


THE  SYMPATHETIC  NERVOUS  SYSTEM. 

A  pair  of  nervous  cords,  situated  one  on  each  side  of 
the  spinal  column,  three  main  "  plexuses  "  in  the  cavity  of 
the  thorax  and  abdomen,  and  a  large  number  of  smaller 
ganglia  widely  distributed  over  the  body,  especially  in 
connection  with  the  veins  and  arteries,  constitute  the 
Sympathetic  Nervous  System.  Each  of  these  nervous  cords 
consists  of  a  number  of  ganglia  united  by  intermediate 
nerves.  In  the  other  regions  of  the  spinal  column  the 
number  of  these  ganglia  equals  that  of  the  number  of 
vertebrae  (see  Fig.  8)  ;  but  in  the  region  of  the  neck  there 
are  only  three  ganglia.  The  three  main  plexuses  are  col- 


34  PHYSIOLOGICAL  PSYCHOLOGY. 

lections  of  nerve-cells  and  a  dense  plexiform  arrangement 
of  nerve-fibres.     One  is  situated  at  the  base  of  the  heart;    -4 
another  in  the  upper  part  of  the  abdominal  cavity;  and 
the  third  in  front  of  the  last  lumbar  vertebra. 

From  the  gangliated  cord,  just  described,  a  communyfl| 
eating  and  a  distributing  series  of  nerve-branches  are  d«T 
rived.     By  the  former  the  sympathetic  system  is  brought 
into  close  anatomical  and  physiological  connection  with  the  __|. 
cerebro-spinal  nervous  system.     The  distributory  branches 
of  nerves  connect  the  gangliated  cord  with  the  viscera  and 
blood-vessels  of  the  body.     A  recent  view  (Gaskell,  in  a 
paper  read  May  24,  1888)  considers  the  so-called  "sympa- 
thetic ganglia,"  not  as  representatives  of  an  independent 
nervous  system,  but  as  belonging  to  the  spinal  system  as  -f 
truly  as  do  the  ganglia  of  the  posterior  roots  (see  Fig.  10). 
But  the  former  differ  from  the  latter  in  being  efferent 
rather  than  afferent;   and  in  that  the  fibres  enter  them 
as  medullated  but  emerge  as  non-medullated. 

The  interest  which  the  sympathetic  nervous  system  has 
for  the  study  of  physiological  psychology  is  largely  indi- 
rect. This  fact  is  partly  due  to  our  comparative  lack  of 
knowledge  respecting  its  more  specific  functions.  It  seems 
to  form  a  bond  between  the  sensations,  emotions,  and  —• 
ideas,  which  have  their  physical  basis  in  the  cerebro-spinal  - 
system,  and  those  organs  in  the  chest  and  abdomen  whose 
condition  is  so  closely  related  to  such  psychical  states. 
The  causes  of  many  vague  sensations  and  feelings,  and  of 
the  coloring  of  the  "background,"  as  it  were,  of  our  life 
in  the  body,  undoubtedly  lie,  partly,  in  the  stimulation  of 
the  nerves  of  this  system  by  the  thoracic  and  visceral 
organs.  The  effect  of  certain  emotions  upon  digestion, 
circulation,  and  other  functions  of  these  organs,  is  too  well 
known  to  require  detailed  statement. 


STRUCTURE   OF   THE   SPINAL   CORD   AND  BRAIN.       35 


THE  CEREBRO-SPINAL  NERVOUS  SYSTEM. 

The  spinal  cord  and  brain  are  the  great  centres  of  the 
Cerebro-spinal  System.  These  masses  of  nervous  matter 
are  situated  in  the  bony  cavity  of  the  spinal  column  and 
the  skull. 

Membranes  of  the  Spinal  Cord  and  Brain.  —  The  cerebro- 
spinal  nervous  substance  has  three  coverings  or  mem- 
branes. These  are  the  dura  mater,  the  arachnoid,  and  the 
pia  neater.  _ — 

(1)  The  membrane  lying  next  to  the  wall  of  the  bony 
cavity  of  the  cerebro-spinal  axis  is  called  "  dura  mater." 
It  is  white,  tough,  fibrous.     In  the  skull  it  becomes  identi- 
cal with  the  inner  lining  of  the  bones.     On  passing  into  the 
spinal  column  it  somewhat  changes  its  character.     It  puts 
forth  three  processes  which  divide  —  although  only  incom- 
pletely—  the  cavity  of  the   skull   into   two   symmetrical 
halves,  and  into  an  upper  and  a  lower  space.     These  pro- 
cesses are  (a)  the  falx  cerebri,  sickle-shaped,  and  extending 
between  the  two  halves  of  the  large  brain;  (6)  the  falx 
cerebelli,  a  similar  process  between  the  two  lateral  lobes  of 
the  cerebellum ;    and  (<?)  the  tentorium  cerebelli,  an  arch 
over  the  cerebellum. 

(2)  The  "arachnoid"  membrane   is   transparent,  com- 
-  posed   of   delicate   connective  tissue.     Toward  the   dura 

mater  it  presents  a  smooth,  firm  surface.  It  is  reflected 
on  to  the  roots  of  the  spinal  and  cranial  nerves.  The 
space  below  this  surface  is  called  "  subarachnoid " ;  it  is 
divided  into  smaller  spaces  by  bundles  of  delicate  tissue, 
and  its  inter-communicating  areas  are  filled  by  an  alkaline 
fluid. 

(3)  The  "  pia  mater  "  is  a  vascular  membrane,  —  a  net- 
work of  fine  branches  of  arteries  and  veins,  held  together 
by  delicate  connective  tissue.     It  closely  invests  the  ner- 
vous substance  of   both  spinal  cord  and  brain;    it  sends 


36  PHYSIOLOGICAL   PSYCHOLOGY. 

prolongations  into  the  fissures  and  columns  of  the  cord, 
and  dips  into  the  fissures  between  the  convolutions  of  the 
brain.  In  this  way  the  minute  blood-vessels  are  brought 
into  the  interior  of  the  nervous  substance. 

These  three  membranes  are  not  themselves  possessed  of 
nervous  functions;  but  by  them  the  nervous  masses  of 
the  cerebro-spinal  axis  are  protected,  held  together,  "  cush- 
ioned," and  nourished  with  blood. 

Cranial  and  Spinal  Nerves.  —  The  cerebro-spinal  axis,  or 
great  central  nervous  mechanism,  is  connected  with  the 
end-organs  of  motion  and  of  sense  by  forty-three  pairs  of 
nerves.  Of  these,  thirty-one  pairs  are  "  spinal  nerves," 
and  twelve  pairs  are  "  cranial "  or  "  encephalic." 

The  thirty-one  pairs  of  spinal  nerves  originate  in  the 
substance  of  the  spinal  cord  and  pass  out  of  the  spinal 
canal  through  openings  called  "  intervertebral  foramina." 
Of  these,  counting  from  above,  the  first  eight  pairs  are 
"  cervical,"  the  next  twelve  "  thoracic  "  or  "  dorsal "  ; 
then  five  "  lumbar,"  five  "  sacral,"  one  "  coccygeal."  Each 
nerve  arises  from  the  side  of  the  cord  by  two  roots,  an 
anterior  and  a  posterior.  The  former  is  composed  of 
—  motor  nerve-fibres.  The  latter  is  composed  of  sensory 
nerve-fibres,  and  has  a  swelling  or  ganglion  upon  it  (see 
Fig.  10).  Immediately  beyond  the  ganglion  the  two  roots 
unite.  The  united  nerve  soon  after  separates  into  two 
divisions,  each  of  which  contains  both  sensory  and  motor 
fibres,  that  are  distributed,  one  upon  the  back  and  the 
other  upon  the  front  and  sides,  to  all  parts  of  the  trunk 
and  limbs. 

The  cranial  nerves  are  divided  by  Continental  authori- 
ties into  twelve  pairs,  and  by  British  authorities  into  nine. 
These  may  be  arranged  in  three  groups :  (1)  the  exclu- 
sively sensory  nerves  ;  -  (2)  the  exclusively  motor  nerves ; 
and  (3)  the  mixed  nerves.  To  the  first  group  belong  the 
olfactory,  the  optic,  and  the  auditory.  To  the  second 


FIG.  8.  — View  of  the  Cerebro-spiual 
Axis.  (After  Bpurgery.)  y5.  TQe  rjght 
half  of  the  cranium  and  trunk  has  been 
removed,  and  the  roots  of  the  spinal  nerves 
dissected  out  and  laid  on  their  several 
vertebrae.  F,  T,  O,  cerebrum;  C,  cere- 
bellum; P,  pons  Varolii;  mo,  medulla 
oblongata;  ms,  ms,  upper  and  lower  ex- 
tremities of  the  spinal  marrow.  CI.  to 
CVIII.  are  cervical  nerves;  DI.  to  DXII., 
dorsal;  LI.  to  LV.,  lumbar;  SI.  to  8V., 
sacral;  Col.,  coccygeal. 


38  PHYSIOLOGICAL  PSYCHOLOGY. 

group  belong  the  nerves  that  supply  the  principal  muscles 
the  eyeball,  the  muscles  of  facial  expression  and  of  the 
tongue,  and  the  so-called  spinal  accessory  nerve.  To  the 
third  group  belong  the  three  nerves  which  are  distributed 
so  widely  over  the  mucous  membranes  and  muscles  of  the 
iace,  tongue,  pharynx,  and  internal  organs,  namely,  the 
trigeminus,  the  glossopharyngeal,  and  the  pneumogastric 
or  vagus  (see  Figs.  15  and  18). 

By  these  pairs  of  peripheral  nerves  the  sensory  areas  of 
the  body  have  the  impulses  originating  in  them  conducted 
to  the  central  nervous  mass,  while  the  motor  areas  are  con- 
trolled from  the  same  central  mass.  Thus  sensation  and  per- 
ception, which  are  dependent  upon  the  excited  condition 
of  the  end-organs  of  sense,  are  made  possible.  And  by 
reflex  and  automatic  action  of  the  cerebro-spinal  axis  both 
involuntary  and  voluntary  movements  of  the  trunk  and 
limbs  are  accomplished  through  the  conducting  nerves. 

STRUCTURE  OF  THE  SPINAL   CORD. 

The  Spinal  Cord  extends  in  the  spinal  canal  from  the 
aperture  (foramen  magnum),  through  which  it  connects 
with  the  brain,  downward  to  opposite  the  body  of  the  first 
lumbar  vertebra.  Here  it  tapers  off  into  a  slender  thread 
of  gray  nervous  substance  (filum  terminate).  Its  length 
is,  in  the  adult,  from  fifteen  to  eighteen  inches.  It  is 
nearly  cylindrical  in  shape,  its  front  and  back  surfaces 
being  somewhat  flattened.  It  has  two  considerable  enlarge- 
ments of  its  girth,  an  upper  (cervical),  from  which  arise 
the  nerves  that  supply  the  upper  limbs,  and  a  lower  (lum- 
bar) which  supplies  the  lower  limbs  with  nerves. 

Fissures  and  Commissures  of  the  Cord.  —  The  spinal  cord 
is  almost  completely  divided  for  its  entire  length  into 
right  and  left  halves  by  two  "  median  "  Fissures  ;  a  some- 
what broader  one  in  front  (anterior),  and  a  somewhat 
deeper  but  narrower  one  behind  (posterior).  Two  bands 


A 


B 


FiG.9.  — A,  Anterior,  and  B,  Posterior,  View 
of  the  Spinal  Cord  and  Medulla  Oblongata.  B', 
the  Filura  terminale,  which  has  been  cut  off  from 
A  and  B.  1,  Pyramids  of  the  medulla,  and  1', 
their  decussation.  2,  olives;  3,  lateral  strands 
of  the  medulla;  4',  calamus  scriptorius;  5,  the 
funiculus  gracilis;  and  6,  the  funiculus  cuneatus; 
7,  the  anterior,  and  9,  the  posterior,  fissures;  8, 
the  antero-lateral  depression ;  10,  postero-lateraj 
groove.  C,  the  cervical,  and  L,  the  lumbar, 
enlargements  of  the  cord. 


10- 


•7 

\L 


40 


PHYSIOLOGICAL  PSYCHOLOGY. 


of  nervous  matter,  called  Commissures,  unite  its  halves 
and  prevent  the  fissures  from  dividing  it  completely.  The 
front  one,  at  the  bottom  of  the  anterior  fissure,  is  the  white 
commissure  ;  the  one  behind,  at  the  bottom  of  the  posterior 
fissure,  is  the  gray  commissure.  The  latter  is  larger  than 
the  former,  except  at  the  cervical  and  lumbar  enlarge- 
ments of  the  cord.  Along  its  entire  length  the  gray  com- 
missure encloses  a  minute  canal  (central  canal). 

Columns  and  Horns  of  the  Cord.  —  Each  half  of  the  cord 
is  subdivided  by  the  entrance  of  the  nerve-roots  into  three 

Columns.  These 
are  (a)  the  ante- 
rior, which  lies 
between  the  ante- 
rior median  fissure 
and  the  anterior 
roots  ;  (6)  the  pos- 
terior, which  lies 
between  the  pos- 
terior median  fis- 
sure and  the  pos- 
terior roots ;  and 
(<?)  the  lateral, 
which  lies  at  the 
side  of  the  cord 
between  the  other 
two  columns. 

FIG.  10.  —  A,  Anterior,  and  B,  Lateral,  View  of  a  Portion  rp 

of  the  Cord  from  the  Cervical  Region.    «/i-     (Schwalbe.)  I KMIS V6IS6    S6C- 

1,  Anterior  median,  and  2,  posterior  median,  fissures.    At  .  .                 />    ,-•                    -, 

3,  is  the  antero-lateral  depression,  over  which  spread  the  tlOUS    Ol    tile     OOTCt 

anterior  roots   (5).-    The  posterior  roots   (6),  with   their  ,              ,      ...            -, 

ganglion  (6'),  arise  from  the  postero-lateral  groove,  and  SHOW  tnat   ItS  SUD- 

uniting  with  the  anterior  roots  form  the  compound  nerve  (7).  _  ., 

stance,     like     all 

nervous  substance,  consists  of  both  white  and  gray  ner- 
vous matter.  The  former  is  external  and  composes  the 
columns  of  the  cord ;  the  latter  is  internal  and  is  sur- 
rounded by  the  white  matter.  The  relative  amount  of  the 


STRUCTURE   OF   THE   SPINAL   CORD  AND   BRAIN.       41 

two  varies  in  different  portions  of  the  cord.  At  the  lower 
end  of  the  cord  scarcely  any  white  matter  is  found ;  the 
amount  of  such  matter  increases  from  below  upwards,  and 
is  largest  in  the  cervical  region.  The  amount  of  gray 
matter  is  greatest  in  the  two  enlargements  of  the  cord. 

The  gray  columns  and  their  commissures  form  a  figure 
somewhat  like  a  Roman  H  or  a  large  X,  or  a  pair  of 
butterfly's  wings.  But  the  lateral  masses  of  these  crescent- 
shaped  bodies  are  narrower  in  the  thoracic  region,  and 
broader  at  the  cervical  and  lumbar  enlargements.  The 
limbs  of  the  figure  thus  formed  are  called  Horns  ;  of  these 
horns  each  side  has  therefore  two,  a  rounded  anterior  and 
a  longer  and  narrower  posterior  horn.  The  division  into 
columns,  fairly  well  marked  on  the  surface,  is  lost  as  we 
pass  into  the  central  gray  matter.  The  anterior  horn 
has  here  an  appearance  of  "  spongy  substance  "  ;  the  pos- 
terior, of  a  kernel  of  such  substance  surrounded  by  "  gelat- 
inous substance." 

White  Substance  of  the  Cord.  —  The  external  or  white 
matter  of  the  spinal  cord,  besides  connective  tissue  and 
lymph-  and  blood-vessels,  is  composed  of  nerve-jibres.  The 
essential  part  of  these  fibres  is  the  axis-cylinder ;  although, 
when  fully  developed,  they  have  also  the  medullary  sheath. 
They  vary  in  size,  the  thickest  being  found  in  the  outer 
portions  of  the  anterior  columns  (y^Vir  to  rAnr  of  an  inch). 
In  the  lateral  columns  the  finer  ones  lie  near  the  gray 
matter;  but  in  the  posterior  columns  they  increase  in 
thickness  as  they  approach  the  posterior  gray  commissure. 

The  direction  of  the  nerve-fibres  in  the  white  substance 
of  the  cord  is  either  vertical,  or  horizontal,  or  oblique. 
The  vertical  fibres  are  most  abundant  and  are  united  into 
fascicles  which  ascend  toward  the  brain.  The  horizontal 
fibres  are  either  commissural  or  fibres  of  the  roots.  The 
fibres  of  the  white  commissure  run  horizontally  along  the 
median  border  of  the  gray  matter  of  the  horns,  and  become 


42 


PHYSIOLOGICAL  PSYCHOLOGY. 


interwoven  with  the  vertical  bundles  of  the  anterior  horns. 
Most  of  them  pass  from  the  substance  of  the  anterior  horn 
of  one  side  across  to  the  anterior  column  of  the  other  side. 
Fibres  of  the  Roots.  —  Much  interest  is  attached  to  the 
determination  of  the  exact  course,  in  the  spinal  cord,  of 
the  fibres  from  its  anterior  and  posterior  roots.  Its  inti- 
mate structure,  as  fitted  for  those  reflex  functions  which 
are  its  peculiar  property  as  an  organ,  is  thus  understood. 
The  details  are  given  differently,  however,  by  different 
observers  with  the  microscope.  Nor  is  this  strange,  since 
the  fibres  of  the  posterior  root,  especially,  divide  into 
bundles  so  minute  and  so  intricately  interwoven  with  the 
vertical  fibres  of  the  posterior  column  that  their  course  is 
extremely  difficult  to  trace. 


fa. 


,-CO.CL 


co.l. 


o.p. 


FIG.  11.  —  Section  of  the  Spinal  Cord  at  the  Level  of  the  Eight  Pair  of  Dorsal  Nerves. 
8/i«  (Schematic,  from  Schwalbe.)  s.a.,  anterior  fissure;  s.p.,  posterior  septum  (or  fis- 
sure); c.a.,  anterior,  and  c.p.,  posterior,  commissures;  c.c.,  central  canal;  co.a.,  anterior 
horn  ;  co.l.,  lateral  horn  ;  co.p.,  posterior  horn  ;  a,  anterior  lateral,  and  6,  anterior 
median,  cells;  c,  cells  of  the  lateral  horn;  d,  columns  of  Clarke;  e,  solitary  cells  of  the 
posterior  horn;  r.a.,  the  anterior,  and  r.p.,  the  posterior,  roots;  /,  bundle  of  fibres  of 
the  posterior  horn;  and./",  bundle  of  the  posterior  column;  /',  longitudinal  fibres  of 
the  posterior  horn;  s.g.R.,  gelatinous  substance  of  Rolando;  /.a.,  anterior,  f.L,  lateral, 
nnd/./j.,  posterior,  columns. 


STRUCTURE   OF   THE    SPINAL    CORD   AND   BRAIN.        43 

Most  recent  authorities  recognize  two  main  divisions  of 
the  fibres  of  the  posterior  root  on  their  entrance  into  the 
spinal  cord.  Of  these,  one,  said  to  be  the  earliest  devel- 
oped, enters  immediately  the  "gelatinous  substance"  of 
the  posterior  horns  and  becomes  lost  in  it,  or  passes  through 
it  to  form  a  connection  with  the  cells  of  the  "  columns  of 
Clarke  "  (see  Fig.  11).  The  other  portion  of  the  fibres  of 
the  posterior  roots,  said  to  be  developed  later,  passes  for 
a  little  way  outside  of  the  gray  matter  along  the  back  part 
of  the  lateral  column,  and  then,  after  running  upward  a 
variable  distance,  buries  itself  in  the  gray  substance  of  the 
posterior  horn. 

The  fibres  of  the  anterior  roots  traverse  obliquely  the 
white  substance  of  the  cord,  and  either  enter  the  gray  matter 
of  the  anterior  horns  on  the  same  side,  or  pass  by  the  an- 
terior commissure  to  the  other  side  of  the  cord,  or  pass  into 
the  lateral  columns  and  the  posterior  horns. 

Gray  Substance  of  the  Cord,  —  The  nerve-fibres  which 
form  the  principal  mass  of  the  gray  substance  of  the 
spinal  cord  are  generally  rion-medullated,  and  frequently 
divide  and  subdivide  to  form  extremely  minute  plexuses. 
Besides  these  elements,  this  substance  contains  large  num- 
bers of  ganglion-cells.  These  cells  are  described  as  multi- 
polar  and  as  regularly  giving  off  the  two  kinds  of  processes 
already  spoken  of  (see  p.  26).  Gerlach  thought  he  could 
trace  the  very  finest  ramifications  of  the  so-called  "  branch- 
ing "  process  of  the  nerve-cells  of  the  cord  until  they  par- 
ticipated in  those  plexuses  of  nerve-fibres  which  he  regards 
as  an  essential  constituent  of  its  gray  substance.  Others 
consider  the  fate  of  these  processes  to  be  still  unknown. 

Many  of  the  nerve-cells  of  the  posterior  horns  are  exceed- 
ingly small,  and  are  distributed  through  the  above-men- 
tioned plexuses  of  minute  nerve-threads.  Indeed,  some  of 
the  most  recent  investigations  have  concluded  that  the 
nuclei  of  the  motor  nerves  in  the  cord  often  run  into  each 


44 


PHYSIOLOGICAL  PSYCHOLOGY. 


other,  and  cannot  be  distinctly  circumscribed.  Character- 
istic groups  of  ganglion-cells  of  different  sizes  also  occur  at 
various  places  in  the  gray  matter  of  the  cord.  In  the 
anterior  horns  of  the  cervical  and  lumbar  regions  there 

are  three  such  groups 
of  large  cells.  One 
other  important  group 
:rc  is  situated  at  the  inner 
angle  of  the  base  of 
the  posterior  horn ; 
and,  in  its  extent  up 
and  down  the  cord, 
it  forms  the  so-called 
"  column  of  Clarke  " 
(see  Fig.  11). 

Tracts  in  the  Spinal 
Cord.  —  It  is  evidently 
of  the  greatest  impor- 
tance to  trace  out 
those  paths  of  ner- 
vous substance  along 

FIG.  12.  —  Section  of   Dorsal   Part  of    the   Spinal    which      the       nerVOUS 
Cord,  showing  the  Gray  Matter  of  the  Horns.    2%. 

(Henle.)  Ca,  anterior  white,  and  Cg.,  gray  comrais-  impulses  may  paSS  in 
sure;  Cc,  central  canal;  v,  vesicular  column;  s,  spongy  *  *  r 

substance  of  the  posterior  horn,  surrounded  by  g,  gelat-    ^Qg  SDilial  COrd 

inous  substance;  Pr,  reticular  process  ;  Ti,  inter- 
median  lateral  tract.  Neither  the  micro- 
scope nor  physiological  experiment,  however,  finds  it 
easy  to  unravel  these  paths.  Two  other  methods  of 
their  determination  are  most  effective ;  and  when  the 
evidence  of  both  coincides,  it  may  be  regarded  as  fairly 
conclusive.  These  methods  are  the  embryological  and 
the  pathological.  The  former  makes  use  of  the  fact  that, 
in  the  development  of  the  spinal  cord,  the  medullary 
substance  of  the  nerve-fibres  in  different  tracts  is  consti- 
tuted at  different  times,  so  as  to  render  them  distinguish- 
able when  viewed  in  cross-section.  The  pathological 


STRUCTURE   OF  THE   SPINAL   CORD  AND   BRAIN.       45 


method  attempts  to  reach  the  same  result  by  tracing  the 
lines  along  which  degeneration  takes  place  when  the  nerve- 
fibres  have  been  separated  from  their 
place  of  origin  and  nourishment. 

By  the  methods  just  described,  two 
principal  tracts,  which  extend  along 
the  greater  part  of  the  cord,  have  been 
made  out.  From  their  upper  con- 
nections they  have  been  named  the 
"  pyramidal "  and  the  "  lateral  cerebel- 
lar."  The  pyramidal  tract  is  trace- 
able down  from  the  anterior  pyramid 
of  the  medulla  oblongata.  It  divides, 
on  entering  the  upper  portion  of  the 
spinal  cord,  into  two  tracts.  Most 
of  its  fibres  cross  over,  well  up  in  the 
cord,  and  pass  down  in  the  back  part 
of  the  lateral  column  as  a  compact 
bundle.  This  crossed  (or  lateral)  part 
of  the  pyramidal  tract  can  be  traced 
as  far  down  as  the  third  or  fourth 
pair  of  sacral  nerves.  Some  of  the 
fibres,  however,  do  not  cross  in  the 
upper  part  of  the  cord.  These  form 
the  uncrossed  (or  anterior)  part  of  the 
pyramidal  tract ;  on  passing  down- 
ward they  gradually  diminish,  and 
cease  in  the  dorsal  region  of  the  cord.  FIG.  13.— sections  through 

the  Spinal  Cord  at  different 

The  direct  lateral  cerebellar  tract  lies  ele^7ti?n8'atov8how  the  tracts 

of  White  Substance.    I.,  ele- 

between  the  lateral   pyramidal   tract 
and  the   outer   surface   of  the   cord. 
It  disappears  in  the  lumbar  region. 
In   the   posterior   white    column 
tract  can  be  traced  as  far  downward 
as   the   middle   of   the  dorsal  region  c 
of  the  cord ;  it  is  called  the  "  tract  (or  column)  of  Goll." 


of   the 

///.,  of  the'sixth;   and  IF.', 
of  the  twelfth,  dorsal  nerves ; 
and  V.,  of  the  fourth  lumbar 
nerves  ;     pv,    uncrossed    (or 
_     anterior)  pyramidal  tract;  ps, 
^    crossed    (or    lateral)   pyram 


46  PHYSIOLOGICAL  PSYCHOLOGY. 

Mechanism  of  the  Spinal  Cord,  —  This  brief  description  of 
the  structure  of  that  nervous  mass  which  lies  within  the 
bony  cavity  of  the  spinal  column  shows  plainly  its  adapta- 
tion to  the  general  purpose  of  conducting  nerve-commotions 
I  up  and  down,  and  of  acting  as  a  series  of  reflex  and, 
possibly,  automatic  centres.  Its  substance  consists  largely 
of  ascending  and  descending  tracts  of  nervous  elements. 
It  is  also  a  pile  of  nerve-centres,  each  one  of  which  may 
have  its  own  peculiar  functions,  but  all  of  which  are  bound 
together  —  up  and  down,  right  and  left,  and  obliquely  — 
so  as  to  act  unitedly  under  control  of  the  central  organs 
lying  above.  It  has  special  local  mechanisms;  yet,  as  a 
whole,  it  is  connected  with  the  general  mechanism  of  the 
cerebro-spinal  axis.  It  is  adapted  to  do  a  great  variety  of 
work,  as  it  were,  by  itself ;  and  yet  it  can  be  made  to  do 
service  under  the  command  of  the  brain.  It  is  also  at 
various  levels  —  thirty-one  in  number  —  bound  by  the  con- 
necting nerve-cords  to  the  end-organs  of  sense  and  motion. 

STRUCTURE  OF  THE  ENCEPHALON. 

The  Encephalon,  or  Brain  in  the  most  extended  sense  of 
the  word,  includes  all  that  mass  which  is  contained  within 

Cb 


Cbl 

-^sss*' 

Mo 

FIG.  14.  — View  of  the  Brain  In  Profile.    y3.     (Henle.)     Cb,  cerebrum ;  Cbl, 
cerebellum;  Mo,  medulla  oblongata;  P,  pons  Varolii. 


STRUCTURE   OF   THE   SPINAL   CORD   AND   BRAIN.       47 


the  cavity  of  the  skull.  On  removing  it  from  this  bony 
cavity  four  divisions  are  apparent  to  any  observer.  Imme- 
diately above  the  section  by  which  it  has  been  separated 
from  the  spinal  cord,  and  appearing  as  an  enlarged  prolon- 
gation of  the  cord,  is  (/)  the  Medulla  Oblongata.  Cov- 
ering the  upper  back  part  of  this  organ,  and  extending 
beyond  it  on  both  sides,  is  (//)  the  Cerebellum,  or  Little 
or  Hinder  Brain.  Swelling  out,  and  in  front  of  the 
medulla,  is  (III)  the  Pons 
Varolii,  or  so-called  "bridge" 
of  the  brain.  While  above 
both  pons  and  cerebellum, 
and  filling  by  far  the  larger 
part  of  the  cranial  cavity, 
when  the  entire  mass  is  in 
its  place,  is  (IV)  the  Cere- 
brum, or  Large  Brain,  —  the 
Brain  proper. 

External  Appearance  of  the 
Medulla  Oblongata.  —  This 
organ  is  somewhat  pyramidal 
in  form,  about  one  and  one- 
fourth  inches  in  length, 

j  i            .f          ,  -I                                 •       i  FIG.  15.  —  Diagrammatic  dissection  of  the 

tnree-IOUrths     tO      One      inch  medulla  oblongata   and  pons   to  show  the 

•i            i  .       .,           .  -i                                -i  course  of  the  fibres,    a,  superficial,  a'   deep 

broad  in  itS  Widest  part,  and  transverse  fibres  of  the  pons;  6,  b,  anterior 

,      ,  ,,  .       T     ,1  .    i          -r,  pyramids  ascending  at  6'  through  the  pons; 

One-hall  inch,  thick.      ItS  an-  c,  c,  olivary  bodies;  c',  olivary  fasciculus  in 

.                          .  7  the  pons;  d,  d,  anterior  columns  of  cord;  e, 

tenor  pyramids  appear  COn-  inner  part  of  the  right  column  joining  the 

.                             •  anterior  pyramid  ;  /,  the  outer  part  going  to 

tmUOUS     With     the     anterior  the  olivary  fasciculus;  g,  lateral  column  of 

.  cord  ;  h,  the  part  which  decussates  at  k,  the 

COlumnS     Of     the     COrd  ;      itS  decussation   of  the   pyramids  ;    I,   the  part 

which  joins  the  restiform  body;  m.that  which 

lateral   area    shoWS    Upon   itS  f  9rras  the  f  asciculus  teres  ;  n.arciform  fibres. 

1  and  2,  sensory  and  motor  roots  of  fifth 

UDDer       end       an       elevation  nerve;  3,  sixth  nerve;  4,  portio  dura;  5,  por- 

Jrjr  tio  intermedia;    6,  portio  mollis  of  seventh 

Called   the  "  Olivary  body  "  ;  nerve;  T.glosso-pharyngeal;  8,  pneumo-gaa- 

*  trie;  9,   spinal  accessory  of  eighth  nerve; 

its  posterior    tracts    appear   10,  nypo-giossai  nerve. 

continuous  with  the  posterior  columns  of  the  cord.     Just 

outside   the    upper   part    of    each    posterior    tract    there 


48  PHYSIOLOGICAL   PSYCHOLOGY. 

ascends  to  the  cerebellum  a  strong  tract  named  the 
"restiform  body."  A  part  of  the  posterior  tract  is  marked 
off  from  the  rest  by  a  septum  of  the  pia  mater ;  this  part 
is  called  funiculus  gracilis,  which,  further  upward,  broad- 
ens out  into  the  clava.  The  back  part  of  the  lateral  area 
also  broadens  out  into  a  wedge-shaped  body,  known  as  the 
cuneate  funiculus.  (For  further  details,  see  Fig.  15.) 

Internal  Structure  of  the  Medulla,  —  An  important  re-dis- 
tribution of  the  nervous  substance,  both  white  and  gray, 
takes  place  in  the  medulla  oblongata.  The  arrangement 
of  the  nerve-elements  thus  becomes  much  more  complex 
than  that  of  the  spinal  cord.  To  understand  this  we  must 
note  chiefly  the  following  particulars :  (1)  The  external 
portions  of  white  substance  on  the  back  part  of  the  organ 
(the  posterior  tracts  and  restiform  bodies)  diverge  and 
become  thinner ;  thus  the  central  gray  mass  is  opened  up 
and  allowed  to  come  to  the  surface  between  the  sides  of 
the  surrounding  white  matter.  (2)  The  great  vertical 
tracts  of  nerve-fibres  from  the  spinal  cord  change  their 
course  greatly,  and  other  new  tracts  from  the  cerebrum  and 
cerebellum  are  gathered  up  within  this  organ,  for  trans- 
mission downward.  (3)  In  this  way  the  central  gray  mass 
of  the  horns  becomes  much  broken,  and  its  distribution 
changed.  A  number  of  large  nuclei  are  also  added  to 
the  nervous  mass  in  this  organ. 

The  attempt  to  trace  the  various  tracts  of  nerve-fibres  as 
they  ascend  through  the  medulla  from  the  columns  of  the 
cord  leads  us  to  notice  :  — 

The  Decussation  of  the  Pyramids,  —  The  external  white 
matter  of  the  medulla  oblongata  is  only  to  a  small  extent 
a  direct  continuation  of  the  columns  of  the  spinal  cord. 
A  large  bundle  of  nerve-fibres,  which  in  the  cord  lies  in  the 
back  part  of  the  lateral  column,  pushes  its  way  obliquely 
through  the  gray  matter  of  the  anterior  horn,  and  passes  in 
front  of  the  central  canal  to  the  pyramid  of  the  opposite 


STRUCTURE   OF   THE   SPINAL   CORD   AND  BRAIN.       49 

side.  The  abrupt  passage  of  so  many  fibres  through  it 
breaks  up  the  anterior  horn,  separates  part  of  it  from  the 
rest,  and  pushes  this  separated  part  over  to  one  side,  and 
close  to  a  part  of  the  posterior  horn.  The  posterior  horn 
also  is  shifted  sidewise  by  the  increased  size  of  the  pos- 


72,  C. 


flct. 


-py" 


FIG.  16. — Section  showing  the  Decussation  of  the  Pyramids  at  the  point  where  the  Spinal 
Cord  passes  into  the  Medulla  Oblongata.  6/i-  (Schwalbe.)  f.l.a.,  longitudinal  anterior 
fissure,  through  which  the  bundles  of  pyramidal  fibres  (py,py'}  are  crossing  over  at 
d;  V,  anterior,  and  S,  lateral  pyramids;  C.a.,  anterior  horn  with  groups  of  ganglion- 
cells,  a  and  6;  cc,  central  canal;  f.r.,  formatio  reticularis;  ce,  the  neck,  and  g,  the  head, 
of  the  posterior  horn;  w.c.,  nucleus  of  the  funiculus  cuneatus;  and  n.g.,  of  the  funi- 
culus  gracilis;  H1,  funiculus  gracilis;  H2,  funiculus  cuneatus;  x,  group  of  ganglion- 
cells. 

terior  tracts ;  it  comes  to  lie  almost  at  right  angles  to  the 
posterior  median  fissure  ;  its  head  enlarges  and  approaches 
to  the  surface,  which  it  pushes  out  into  a  projection  (funi- 
culus of  Rolando)  and  higher  up,  into  a  distinct  swelling 
(tubercle  of  Rolando). 

Tracing  the  principal  bundles  of  fibres  from  the  spinal 
cord  through  the  medulla  gives  the  following  result :  The 
posterior  column  of  the  cord  forms  the  substance  of  the 


50 


PHYSIOLOGICAL   PSYCHOLOGY. 


three  posterior  strands  of  the  medulla;  namely,  gracilis, 
cuneatus,  and  funiculus  of  Rolando.  A  great  part  of  the 
lateral  column  (the  lateral  pyramidal  tract)  passes  into 
the  opposite  pyramid  of  the  medulla,  and  ascends  toward 
the  cerebrum.  Another  part  (the  direct  lateral  cerebellar 
tract)  passes  by  the  middle  of  the  organ,  obliquely  back- 
ward to  the  restiform  body ;  but  the  remainder  of  it  dips 
under  the  olives  and  continues  upward.  Most  of  the  an- 
terior column  of  the  cord  dips  under  the  pyramid  of  the 

medulla  and  passes  up- 
ward toward  the  cerebrum; 
but  part  of  it  continues 
into  the  pyramid  of  the 
same  side  (see  Fig.  15). 

Formatio  Reticularis  and 
Nuclei  of  the  Medulla.  — 
By  the  "  decussation  of 
the  pyramids "  the  sub- 
stance of  the  anterior 
horns  of  the  medulla  is 
broken  up  into  a  coarse 
network  (formatio  reticu- 
laris), containing  nerve- 
cells  intersected  by  bun- 
dles of  fibres.  Four  special 


fl.a.  -fa., 

FIG.  17.  —  Section  showing  Gray  Matter  of  the 
Medulla  Oblongata,  in  the  region  of  the  upper 
crossing  of  the  Pyramids.  4/i-  (Schwalbe.)/.Z.a., 


.     i-  ....,  „  . 

anterior,  and  s.l.p.,  posterior,  fissures  ;  n.XI.     nuclei,    OI     gelatlUOUS 
and  n.XI  I.,  nuclei  of  the  vagus  accessorius  and 
hypoglossal  nerves  ;  d.a.,  so-called  upper  cross- 


ing  of  the  pyramids  ;  py,  anterior  pyramid  in 
which  is  n.ar,  the  nucleus  arciformis  ;  o,  begin- 
ning  of  the  olivary  nucleus  ;  <A,  accessory  oli- 
vary nucleus  ;  F.r.,  formatip  reticularis  ;  g, 
substantia  gelatmosa  ;  /.a.,  /.a1,  /.a.2,  arciform 

fibres- 


. 
,    and    Containing 

multlDOlar  nerVC-Cells,  are 
to    be    noted   in    each    half 

of  the  medulla;  these 
are  the  nucleus  arciformis,  the  nucleus  olivaris  or  "  dentate 
body,"  the  nucleus  olivaris  accessorius,  and  the  nucleus  pyra- 
midalis"  sometimes  called  "  inner  accessory  nucleus  " 
(see  Fig.  17).  Other  nuclei  consist  of  those  groups  of 
multipolar  cells  to  which  the  "  roots  of  origin  "  of  certain 


STRUCTURE   OF   THE   SPINAL  CORD   AND   BRAIN.       51 

cranial  nerves  are  traced.  These  nerve-nuclei  receive  their 
names  from  the  nerves  whose  fibres  are  supposed  to  origi- 
nate in  them. 

External  Appearance  of  the  Cerebellum.  —  In  the  Cere- 
bellum the  general  arrangement  of  the  two  kinds  of  ner- 
vous matter  is  the  reverse  of  that  of  the  spinal  cord  and 
the  medulla  ;  the  gray  matter  is  outside,  the  white  within. 
This  organ  may  be  described  as  a  white  or  medullary  mass, 
composed  of  three  pairs  of  large  stalks  of  nerve-fibres,  en- 
veloped in  a  wrinkled  covering  of  gray  nervous  substance. 
These  three  stalks  are  called  the  "  peduncles  "  or  "  crura  " 
of  the  cerebellum;  they  serve  to  connect  it  with  three 
other  organs,  with  parts  of  which  they  are  continuous. 
They  are  called  (1)  the  inferior  peduncle,  which  is  identical 
with  the  restiform  fascicle  as  it  ascends  from  the  medulla 
to  the  cerebellum ;  (2)  the  superior  peduncle,  which  con- 
nects the  cerebellum  forward  (with  the  tegmentum  of  the 
crus)  ;  and  (3)  the  middle  peduncle,  which  passes  down 
on  the  side  into  the  pons  (see  Figs.  18  and  19). 

The  surface  of  the  cerebellum  shows  two  hemispheres 

J 


FIG.  18. —Lower  Surf  ace  of  Cerebellum.  2/s.  (After  Sappey.)  1,  inferior  vermiform 
process  ;  2,  2,  vallecula  ;  5,  flocculus  ;  6,  pons  Varolii  ;  8,  middle  peduncle  of  the  Cere- 
bellum ;  9,  medulla  oblongata.  Various  pairs  of  nerves  are  seen  thus  :  12  and  13,  roots 
of  fifth  pair  ;  14,  sixth  pair  ;  15,  facial  nerve  ;  17,  auditory  ;  18,  glossopharyngeal  ;  19, 
pneumogastric  ;  20,  spinal  accessory  ;  21,  hypoglossal. 


52  PHYSIOLOGICAL  PSYCHOLOGY. 

or  lateral  lobes,  united  by  a  central  lobe  called  the  vermi- 
form process.  The  central  lobe,  on  its  upper  surface,  is 
a  mere  elevation  ;  but  on  its  lower  surface,  where  it  lies 
at  the  bottom  of  a  deep  depression  (yallecula),  its  "  ver- 
miform" character  is  well  defined.  The  surfaces  of  the 
cerebellum  are  divided  by  fissures  into  smaller  lobes  or 
lobules. 

Internal  Structure  of  the  Cerebellum,  —  The  interior  rela- 
tions of  the  nerve-fibres  of  the  peduncles  of  this  organ 
are  extremely  intricate,  and  are  not  known  in  much  detail. 
United  in  a  white  core,  they  form  a  rather  uniform  mass 
which  is  interrupted,  however,  by  certain  nuclei  of  a 
gelatinous  appearance.  Several  bodies  of  gray  matter  are 
found  in  this  core ;  of  these  the  more  important  is  dis- 
closed by  cutting  through  a  little  to  the  outside  of  the 
central  lobe.  This  body  (the  corpus  dentatum  of  the  cere- 
bellum) is  arranged  like  the  dentate  body  of  the  medulla. 

The  gray  matter  of  the  cortex,  or  rind,  of  the  cerebellum 
is  constructed  in  a  peculiar  manner.  It  consists  of  thin 
plates  (Lamellae}  of  gray  substance,  which  are  penetrated 
by  prolongations  of  the  white  matter  of  the  core.  The 
branches  of  the  white  matter  within  the  plates  of  gray  sub- 
stance impart  to  it  an  arborescent  appearance,  and  lead  to 
the  name  of  "arbor  vitse "  (see  Fig.  19).  In  the  cortex 
itself  three  distinct  layers  may  be  distinguished:  (1)  an 
external  " molecular  layer"  having,  in  a  framework  of 
connective  tissue,  a  few  roundish  cells  and  minute  fibres ; 
(2)  an  internal  layer,  which  merges  gradually  into  the 
substance  of  the  core,  and  contains  multitudes  of  granules 
whose  nature  is  in  doubt;  and  (3)  a  middle  layer  com- 
posed of  a  single  irregular  row  of  large  ganglion-cells, 
called  "  cells  or  corpuscles  of  Purkinje."  Comparatively 
large  processes  from  these  cells  appear  to  ramify  within 
the  outer  layer. 

Structure  of  the  Pons  Varolii,  —  The  Pons,  or  "  Bridge  of 


STRUCTURE   OF   THE   SPINAL   CORD  AND   BRAIN.       53 

the  Brain,"  is  a  thickening  of  the  ventral  wall  of  the  fourth 
ventricle,  composed  of  the  middle  peduncles  of  the  cere- 
bellum encircling  and  blending  with  the  continuation 
upward  of  the  medulla.  The  general  direction  of  its 


FIG.  19.  —  Median  Section  through  the  Stem  of  the  Brain.  (After  Reichert.)  M,  me» 
dulla  oblongata  ;  of  which  Pa  are  the  pyramids,  decussating  at  pd ;  c,  central  canal  ; 
pp,  restiform  "body  ;  Pv,  pons  Varolii  ;  F4,  fourth  ventricle  ;  av,  arbor  vitae  of  the  cere- 
bellum ;  p,  pyramid  ;  u,  uvula  ;  n,  nodule  ;  as,  aqueduct  of  Sylvius  ;  Cr,  crus  cerebri  ; 
Q,  corpora  quadrigemina  ;  P,  pineal  gland  ;  Th,  optic  thalamus.  Commissures :  ca,  the 
anterior  ;  cm,  the  mollis  ;  and  cp,  the  posterior,  F3,  the  third  ventricle  ;  A,  corpus 
albicans  ;  tc,  tuber  cinereum  ;  i,  infundibulum. 

superficial  fibres  is  transverse,  though  the  lower  ones 
ascend  slightly  and  the  superior  ones  descend  somewhat 
obliquely.  On  removing  these  superficial  fibres  the  pro- 
longed fibres  of  the  pyramids  are  exposed  to  view ;  these, 
as  they  ascend  through  the  pons,  are  intersected  by  trans- 
verse fibres. 

Nuclei  of  gray  matter  are  found  everywhere  between 
the  fibres  of  the  ventral  part  of  the  pons.  The  back  part 
of  the  organ  is  chiefly  constituted  by  a  continuation  up- 
ward of  the  formatio  reticularis,  and  of  the  gray  matter  of 
the  medulla.  Several  important  collections  of  nerve-cells 
lie  embedded  in  this  reticular  formation ;  the  principal  of 


54  PHYSIOLOGICAL  PSYCHOLOGY. 

these  is  the  "  superior  olivary  nucleus."  Other  nuclei  in 
this  region  give  origin  to  the  seventh  or  facial  nerve,  and 
to  portions  of  the  fifth  nerve. 

Structural  Significance  of  the  Lower  Parts  of  the  Brain.  — 
The  very  formation  of  the  organs  which  have  just  been 
described  is  indicative  of  their  service  in  the  mechanism 
of  the  cerebro-spinal  axis.  This  service  may  be  said  to  be 
of  three  kinds.  They  constitute  the  paths  over  which  the 
nerve-commotions  are  to  run  between  the  upper  brain  and 
the  spinal  cord.  They  also  serve  as  organs  in  which  the 
roots  of  origin  of  important  pairs  of  cranial  nerves  may  be 
planted.  And  closely  connected  with  these  functions  is 
their  peculiar  adaptability  to  act  as  central  organs.  They 
are  arranged  more  elaborately  than  the  spinal  cord,  and  in 
more  immediate  connection  with  the  brain  and  the  higher 
organs  of  sense  —  so  as  to  perform  various  reflex  and  auto- 
matic functions.  But  while  they  share  in  these  general 
characteristics  of  structure,  they  have  peculiarities  belong- 
ing to  each. 

The  medulla  oblongata  is  obviously  an  organ  of  con- 
duction between  the  spinal  cord  below  and  the  parts  of 
the  brain  lying  above  itself.  Its  peculiarities  in  dis- 
charging this  office  are  twofold.  The  nerve-tracts  from 
above  are  greatly  compacted,  are  gathered  together  —  as 
it  were  —  into  shape  to  be  further  compressed  within  the 
spinal  cord.  The  nerve-tracts  from  below,  on  the  other 
hand,  are  broken  up  and  distributed  to  the  side  into  the 
cerebellum  and  into  the  principal  parts  of  the  crura  cerebri. 
Moreover,  a  great  amount  of  crossing  of  the  nerve-tracts 
takes  place  in  this  organ.  This  is  significant  of  the 
important  fact  that  certain  functions  belonging  to  the 
trunk  and  limbs  of  the  body  are  to  be  connected  with 
the  opposite  side  of  the  higher  central  organs.  It  indicates 
that  "right-handed"  man  is  "left-brained."  But  the 
enlarged  and  varied  bodies  of  gray  nervous  substance 


STRUCTURE  OF  THE   SPINAL  CORD  AND  BRAIN.       55 

which  the  medulla  contains  show  that  it  is  "  packed,"  as 
it  were,  with  centres  for  the  discharge  of  reflex  and  auto- 
matic functions  of  the  lower  sort.  Some  of  these  would 
appear  to  be  under  the  immediate  control  of  the  brain 
above,  and  others  not. 

The  cerebellum  is  certainly  an  organ  of  very  striking 
structure.  It  has,  in  its  white  core  and  three  pairs  of  — 
peduncles,  the  mechanism  of  a  conducting  organ.  But  its 
many  masses  of  internal  gray  substance  and  its  gray  cortical 
matter  plainly  show  that  it  is  a  great  central  organ  as  well. 
In  the  aspect  of  an  organ  for  conduction,  its  peculiarity  is 
that  it  is  so  much  to  one  side  of  the  cerebro-spinal  axis. 
It  lies  —  like  an  immense  system  of  Y-tracks  —  out  of  the 
course  of  the  direct  lines,  and  yet  bound  by  nervous  con- 
nections with  all  the  other  organs  of  the  encephalon.  As 
a  central  organ  it  resembles,  far  more  closely  than  any  of 
its  neighbors,  that  crowning  nervous  mechanism,  which  is 
called  pre-eminently  the  Brain. 

The  pans  Varolii  appears  to  be  chiefly  an  organ  for  con- 
densing and  re-distributing  the  nerve-tracts  which  it  con- 
ducts. But  its  structure  is  that  of  a  central  mechanism 
as  well. 

MORE  DETAILED  DESCRIPTION  OF  THE  CEREBRAL  ORGANS. 

That  portion  of  the  encephalic  contents  which  is  called 
the  Cerebrum  or  Large  Brain  much  exceeds  in  size  all  of 
the  rest.  Besides  the  convoluted  surface,  it  contains 
within  its  base  certain  great  ganglia  ;  and  a  number  of 
other  nervous  masses  also  appear  here.  It  is  of  general 
ovoid  shape,  and  is  divided  —  above,  in  front,  and  behind 
—  into  two  halves  or  "hemispheres,"  by  a  deep  longitudi- 
nal fissure.  If  these  hemispheres  are  drawn  asunder,  they 
are  seen  to  be  connected  by  a  broad  white  band  of  nervous 
matter  (the  corpus  callosum).  The  processes  of  the  dura 
mater  which  separate  the  two  halves  (falx  cerebri),  and 


56 


PHYSIOLOGICAL   PSYCHOLOGY. 


which  separate  them  both  from  the  cerebellum  (Untorivm), 
have  already  been  described  (p.  35). 

Under  Surface  of  the  Cerebrum.  —  From  the  front  of  the 


Let 


Pec 


Tbo 


Cba 


Tc 


Spa 


FIG.  20.  —Under  Aspect  of  the  Brain.  (Hcnle.)  B,  basis  of  the  crura  cerebri ;  Cca,  cor- 
pora albicantia;  I1,  olfactory  bulb;  II1,  optic  tract;  Tc,  tuber  cinereuru;  Lpp,  posterior 
perforated  space;  Ccl,  corpus  callosum;  Let,  lamina  cinerea  terminalis;  Spa,  anterior 
perforated  space;  T,  tegraentum;  Tho,  thalamus  opticus;  P,  pons;  Mo,  medulla  oblon- 
gata;  I.  to  VIII.,  first  to  eighth  pair  of  cranial  nerves. 

pons  very  large  white  nerve-cords  are  seen  passing  upward 
and  forward  to  the  cerebrum  from  the  organs  lying  below 
("cerebral  peduncles"  or  crura  cerebri).  Around  each  of 
these  cords  winds  a  flat  band,  the  optic  tract;  these  tracts 


STRUCTURE   OF   THE  SPINAL   CORD  AND   BRAIN.       57 

come  together  in  front  to  form  the  optic  commissure,  from 
which  the  two  optic  nerves  arise.  On  each  side  of  the 
deep  longitudinal  fissure  stretches  the  olfactory  tract,  end- 
ing in  its  bulb.  The  intercranial  part  of  this  nerve  is 
really  a  projecting  portion  of  the  brain.  (For  the  other 
bodies  on  this  surface,  see  Fig.  20.) 

Upper  Surface  of  the  Cerebrum.  —  On  top,  the  cerebral 
hemispheres  present  the  appearance  of  gray  nervous 
matter  arranged  in  folds,  called  "  convolutions  "  or  gyri. 
These  are  separated  by  "  fissures  "  or  sulci,  of  varying 
depth.  A  considerable  difference  exists  in  the  develop- 
ment of  the  different  convolutions,  and  in  the  strength  with 
which  the  different  fissures  are  marked.  The  details  of 
this  aspect  of  the  brain  vary  in  each  individual,  and  even 
in  the  two  hemispheres  of  the  same  brain.  Some  sulci 
and  their  corresponding  gyri  appear  with  a  marked 
regularity  in  the  more  fundamental  stages  of  the  foetal 
brain.  They  have  been  divided  therefore  into  primary, 
secondary,  and  even  tertiary,  classes. 

Lobes  of  the  Cerebrum.  —  By  means  of  the  primary  sulci 
the  hemispheres  of  the  brain  have  been  "  mapped  out "  into 
five  territories,  called  Lobes.  These  are  the  (1)  Frontal,  (2) 
Parietal,  (3)  Temporal  or  Sphenoidal,  or  Tempero-sphe- 
noidal,  (4)  Occipital,  and  (5)  Central  or  Insula,  or  Island 
of  Reil.  The  frontal  lobe  is  divided  from  the  parietal,  on 
its  upper  and  lateral  surface,  by  the  Fissure  of  Rolando 
(sulcus  centralis) ;  and  on  its  lower  surface  from  the  tem- 
poral lobe  by  the  horizontal  branch  of  the  Fissure  of 
Sylvius.  The  parietal  lobe  is  divided  from  the  temporal, 
for  the  greater  part,  by  the  Fissure  of  Sylvius,  and  from 
the  occipital  lobe,  on  its  median  surface  completely,  and 
on  its  upper  surface  only  very  incompletely,  by  the  parie to- 
occipital  fissure.  The  temporal  lobe  is  separated  from  the 
frontal  and  parietal  as  already  described;  but  the  boun- 
dary between  it  and  the  occipital  lobe  is  very  ill-defined. 


58 


PHYSIOLOGICAL  PSYCHOLOGY. 

a. 


FIG.  22. 

FIGS.  21  and  22.  —  Profile  and  Vertex  Views  of  Cerebrum.  Fr,  the  frontal  lobe ;  Par, 
parietal;  Oc,  occipital;  Ts,  temporo-sphenoidal  lobe;  S,  S,  Sylvian  fissure-;  R,  R,  fissure 
of  Rolando;  PO,  parieto-occipital  fissure;  IP,  intra-parietal  fissure ;  P,  P,  Parallel"  fissure; 
SF and  IF,  supero  and  infero-frontal  fissures;  1,  1,  1,  inferior,  2,  2,  2,  middle,  and  3,  3,  3, 
superior  frontal  convolutions;  4,  4,  ascending  frontal  convolution;  5,  5, 5,  ascending  parie- 
tal, 5',  postero-parietal,  and  6,  6,  angular  convolutions;  A,  supra-marginal,  or  convolu- 
tion of  the  parietal  eminence;  7,  7,  superior,  8,  8,  8,  middle,  and  9,  9,  9,  inferior  temporo- 
sphenoidal  convolutions;  10,  superior,  11,  middle,  and  12,  inferior  occipital  convolutions; 
af  0»  Vi  5,  four  annectent  convolutions. 


STRUCTURE   OF   THE  SPINAL   CORD   AND  BRAIN.        59 

The  Island  of  Reil  lies  concealed  beneath  the  frontal,  pari- 
etal and  temporal  lobes ;  it  consists  of  a  few  short  convolu- 
tions which  may  be  disclosed  by  drawing  aside  the  margin 
of  the  Fissure  of  Sylvius.  In  describing  the  other  lobes 
the  boundaries  of  the  occipital  lobe  have  been  sufficiently 
denned. 

Sulci  and  Gyri  of  the  Upper  Surface.  —  The  frontal,  tem- 
poral, and  occipital  lobes  all  have  three  principal  con- 
volutions arranged  in  nearly  parallel  tiers  (superior, 
middle,  and  inferior).  On  each  side  of  the  Fissure  of 
Rolando  are  the  two  central  convolutions,  sometimes 
called  "ascending  frontal"  and  "ascending  parietal." 
Among  the  sulci,  the  Fissure  of  Sylvius  is  much  the  most 
important.  It  exists  in  the  foetal  brain  at  the  third  month, 
and  is  made  by  folding  the  entire  hemisphere  into  an 
arch.  The  Fissure  of  Rolando  is  also  always  present  in 
the  human  brain,  and  is  rarely  or  never  bridged  over  by  a 
secondary  gyrus.  It  appears  in  the  foetus  as  early  as  the 
end  of  the  fifth  month.  (For  further  details,  see  Fig.  22.) 

Median  Aspect  of  the  Cerebrum.  —  On  this  aspect  of  each 
hemisphere  appears  an  important  convolution  which  arches 
around  the  corpus  callosum,  and  is  separated  from  the  first 


FIG.  23.  —  Convolutions  of  the  Inner  and  Tentorial  Surfaces  of  the  Left  Hemisphere. 
t ,  t,  i,  calloso-marginal  fissure;  I,  I,  calcarine  fissure;  m,  m,  hippocampal  fissure;  n,n, 
collateral  fissure;  PO,  parieto-occipital  fissure;  17,  17,  marginal  convolution;  18,  18, 
gyrus  fornicatus;  18',  quadrilateral  lobule;  19,  hippocampal  gyrus;  19',  its  recurved 
end;  25,  occipital  lobule;  9,  9,  inferior  temporo-sphenoidal  convolution. 


60  PHYSIOLOGICAL  PSYCHOLOGY. 

frontal  convolution  by  a  deep  and  constant  fissure  (the 
sulcus  calloso-marginalis)  ;  it  is  called  from  its  shape,  gyrus 
fornicatus.  Its  back  end  curves  downward  and  forward 
under  the  name  of  gyrus  hippocampi,  to  the  inner  tip  of 
the  temporal  lobe.  The  passage  without  break  of  one  of 
these  convolutions  into  the  other  is  considered  by  Ecker 
to  be  a  most  important  difference  between  the  hemispheres 
of  the  brain  of  man  and  those  of  the  ape.  (For  further 
details,  see  Fig.  23.) 

Spaces  and  Bodies  within  the  Cerebral  Mass.  —  By  cutting 
off  successive  slices  of  the  cerebral  hemispheres  their 
general  internal  structure  may  be  exposed.  Beneath  the 
corpus  callosum,  and  roofed  over  by  it,  is  a  space  in  the 
interior  of  each  hemisphere.  These  cavities  are  called 
lateral  ventricles.  They  are  separated  by  a  thin  trans- 
parent wall  (the  septum  lucidum),  and  are  moistened  by  a 
serous  fluid.  The  roof  of  another  cavity,  the  third  ventri- 
cle^ is  formed  by  an  expanded  fold  of  the  pia  mater  (velum 
interpositum).  Each  lateral  ventricle  has  a  central  space 
and  three  curved  prolongations,  or  cornua,  (the  anterior, 
the  posterior,  and  the  descending,)  which  extend  into  the 
cerebral  mass. 

On  the  floor  of  each  lateral  ventricle  the  exposed  por- 
tions of  the  great  "basal  ganglia"  of  the  cerebrum  are 
visible.  Two  large  pear-shaped  bodies  of  gray  color  are 
here  seen,  with  their  broad  extremities  directed  forward 
into  the  anterior  cornua  of  the  ventricle,  and  their  narrow 
ends  outward  and  backward.  They  are  called,  from  their 
striped  appearance  when  cut  open,  "striate  bodies"  or 
corpora  striata.  Between  the  diverging  portions  of  these 
bodies  are  certain  ovoid  masses  called  "  optic  thalami." 
Each  thalamus  rests  upon  one  of  the  crura  cerebri ;  on  its 
outer  and  back  part  are  two  small  elevations  (corpora 
geniculata,  internum  and  externum).  Along  the  floor  of  the 
descending  cornu  of  the  ventricle,  the  inner  surface  of  the 


STRUCTURE   OF   THE  SPINAL  CORD   AND   BRAIN.       61 

gyrus  fornicatus,  doubled  upon  itself  like  a  horn,  appears 
as   a  white   eminence    (hippocampus  major  or  "horn   of 


PIG.  24.  — Basal  Ganglia  of  the  Cerebrum  seen  from  above.  (Henle.)  Ccl,  genu  of  the 
corpus  callosum;  Cs,  corpus  striatum;  Vsl,  ventricle  of  the  septum  lucidum;  Cf,  column 
of  the  fornix;  St,  stria  terminalis;  Tho,  optic  thalamus;  and  Ts,  its  anterior  tubercle ; 
Com,  middle  commissure  between  the  thalami  and  over  the  third  ventricle;  Pv,  pulvinar; 
On,  conarium  or  pineal  gland;  Cop,  corpus  quadrigeminum. 

Ammon  ").  An  arch-shaped  band  of  nerve-fibres,  called 
the  "  fornix,"  is  situated  beneath  the  corpus  callosum.  It 
consists  of  two  lateral  halves  which,  in  front,  form  two  pil- 


62  PHYSIOLOGICAL   PSYCHOLOGY. 

lars  that  descend  to  the  base  of  the  cerebrum  and  become 
the  corpora  albicantia.  Behind  and  between  the  optic 
thalami,  and  resting  on  the  back  surface  of  the  crura 


FIG.  25.  — A  Deeper  Dissection  of  the  Lateral  Ventricle,  and  of  the  Velum  Interposi- 
tura.  a,  under  surface  of  corpus  callosum,  turned  back;  b,  b,  posterior  pillars  of  the 
fornix,  turned  back;  c,  c,  anterior  pillars  of  the  fornix;  d,  velum  interpositum  and  veins 
of  Galen;  e,  fifth  ventricle;  /,/,  corpus  striatum;  g,  g,  taenia  semicircularis;  h,  h,  optic 
thalamus;  k,  choroid  plexus;  I,  taenia  hippocampi ;  m,  hippocampus  major  in  descending 
coruu;  n,  hippocampus  minor;  o,  emineutia  collateralis. 

cerebri,  are  four  eminences  in  two  pairs,  called  corpora 
quadrigemina ;  the  front  pair  are  the  nates ;  the  back  pair, 
testes. 

The  structure  of  some  of  the  bodies  already  referred  to 
requires  a  yet  more  detailed  description,  in  order  to  even 
an  elementary  knowledge  of  the  superior  cerebro-spinal 
mechanism. 


STRUCTURE   OF   THE   SPINAL   CORD   AND   BRAIN.       63 

The  Crura  Cerebri.  —  These  strong  peduncles  of  the 
brain  ascend  from  the  pons  to  the  optic  thalami  and  the 
stria te  bodies.  The  fibres  which  constitute  them  are 
arranged  in  two  groups,  separated  by  the  gray  matter  of 
the  substantia  nigra.  The  front 
portion  is  called  crusta.  Of  its 
fibres  an  important  part  is  contin- 
uous with  the  longitudinal  fibres 
from  the  pyramids  of  the  medulla ; 
it  receives  other  fibres  from  the 
substantia  nigra.  Many  of  the 

fihrp«     nf       fhp     r>rn«ta       run      fn     fhp       the     Mid-brain.      (Schwalbe.) 

nores   01     tne   crubta    run    to   tne     «g.,  aqueduct  of  Sylvius;  s.n., 
nuclei    of    the   striate    bodies   and     o?bthaelltS-u8nifer?eb/'  "S? 
terminate  there;   but   some  radiate     men '™ «f the cru. ceWri. 
upward  through  the  internal  capsule  directly  to  the  cere- 
bral cortex. 

The  back  portion  of  the  crus  is  called  tegmentum.  Some 
of  its  fibres  come  from  the  anterior  column  of  the  cord 
and  radiate  upward  to  the  optic  thalami.  These  fibres  are 
diffused.  Others  are  collected  into  more  well-defined 
tracts,  —  especially  a  tract  coming  from  the  superior  pe- 
duncle of  the  cerebellum,  and  passing  forward  over  the 
anterior  end  of  the  fourth  ventricle  (see  Fig.  19). 

The  formatio  reticularis  is  continued  into  the  tegmen- 
tum, and  some  fibres  appear  to  arise  in  its  cells. 

The  Striate  Bodies.  —  Each  corpus  striatum  consists  of 
two  masses,  the  upper  one  of  which  (nucleus  caudatus) 
projects  into  the  lateral  ventricle ;  the  lower  one  (nucleus 
lenticularis)  is  embedded  in  the  white  substance  of  the 
hemisphere,  and  constitutes  the  principal  part  of  the  body. 
These  two  are  separated  by  an  important  layer  of  white 
matter  called  the  "  internal  capsule." 

The  details  of  the  structure  of  the  striate  bodies  are 
insufficiently  made  out.  The  nucleus  caudatus  receives 
from  the  capsule,  on  the  side  turned  toward  it,  several 


64 


PHYSIOLOGICAL   PSYCHOLOGY. 


bundles  of  fibres.  All  parts  of  the  nucleus  lenticularis 
are  pervaded  with  bundles  of  white  fibres.  Some  bundles 
pass  into  it  from  the  adjacent  parts  of  the  capsule  ;  some 
connect  It  with  the  caudate  nucleus;  some  radiate  from 
it  toward  the  cerebral  cortex.  The  gray  matter  of  this 
organ  has  free  nerve-nuclei  distributed  through  it. 

The  striate  bodies  have  apparently  a  special  connection 

with  the  frontal  and  parietal 
lobes,  but  also  with  some  con- 
volutions of  the  temporal  lobe 
and  the  Island  of  Reil. 

The  Optic  Thalami.  —  The 
gray  matter  of  this  organ  is 
subdivided  into  several  parts, 


Hinttrtr 
Ikeil  det 

Xucleut 
ca<i<lat«i 


Corn  ti 
fOiterius 


Claustrum 


FIG.  27. 


FIG.  28. 


These  and  the  following  two  Figures  show  the  arrangement  of  the  white  and  gray 
substance  in  the  interior  of  the  cerebrum.     (All  four  are  from  Gegenbaur.) 

FIG.  27.  — Horizontal  Section  through  the  Right  Hemisphere. 

FIG.  28.  — Frontal  Section  through  the  Cerebrum  in  front  of  the  Fornix.    Posterior 
surface  of  the  section  displayed. 

so  that  two  or  more  nuclei  are  distinguished  by  different 
authorities.  This  subdivision  is  only  partial,  however ;  the 
organ  is  therefore,  perhaps,  best  described  as  a  mass  of  gray 
nervous  substance,  with  multipolar  and  fusiform  cells,  and 
everywhere  traversed  by  nerve-fibres.  Its  external  and 


STRUCTURE   OP   THE    SPINAL   CORD   AND   BRAIN.        65 

under  surfaces  are  not  free,  but  are  united  with  other  parts 
of  the  brain. 

On  the  outer  surface  of  the  optic  thalami  is  the  white 
matter  of  the  internal  capsule,  composed  of  fibres  diverg- 
ing from  the  crusta  into  the  hemispheres.  With  these 
fibres  mingle  those  which  radiate  from  the  interior  of  the 
organ  itself.  According  to  a  recent  authority,  the  thala- 
mus  is  the  primary  centre  of  the  optic  nerve. 


FIG.  29.  FIG.  30. 

FIG.  29.  — Frontal  Section  through  the  Right  Hemisphere  of  the  Cerebrum  in  front  of 
the  Conimissura  Mollis.  Posterior  surface  of  section  displayed. 

FIG.  30.  — Frontal  Section  through  the  Cerebrum  back  of  the  Commissura  Mollis. 
Front  surface  of  section  displayed. 

The  Corpora  Quadrigemina.  — In  the  interior  of  the  front 
pair  the  most  characteristic  portion  of  this  organ  is 
found;  it  is  a  layer  of  fine  nerve-fibres  running  longitu- 
dinally, between  which  are  small,  scattered  nerve-cells.  In 
the  external  strata  of  these  bodies  multipolar  cells  are 
abundant ;  in  the  interior,  at  the  sides  of  the  Sylvian 
aqueduct,  is  a  collection  of  gray  matter  which  is  continu- 
ous with  the  lining  of  the  third  ventricle.  The  third  and 
fourth  nerves  originate  in  the  nervous  substance  which 
lies  along  this  "  Aqueduct "  (see  Fig.  20). 

Layers  of  the  Cerebral  Cortex.  —  The  general  arrangement 
of  gray  nervous  substance  upon  the  surface,  and  of  white 


66 


PHYSIOLOGICAL  PSYCHOLOGY. 


matter  within,  is  adhered  to  in  all  parts  of  the  cerebral 
cortex.     But  the  form  and  distribution  of  the  nerve-cells 


lllllll J 

*llliIliiK£^;E  'f\ 


FIG.  31.  —  Section  through  the  Cerebral  Cortex  of  Man,  prepared  with  Osmic  Acid.  ^/v. 
(Schwalbe) .  I,  principal  external,  and  II,  internal,  layer ;  x,  layer  lying  as  a  limit  between 
the  two;  m,  medullary  substance  sending  out  bundles  of  nerve-fibres  into  //;  1,  layer 
poor  in  cells,  but  with  an  external  plexus  of  nerve-fibres  (la} ;  2,  layer  of  small,  and  3, 
of  large,  pyramidal  cells;  4,  inner  layer  of  small  nerve-cells. 

are  different  in  different  regions  and  in  different  layers  of 
the  same  region.  As  a  rule  the  cortex  has  five  layers  or 
lamince.  The  entire  thickness  is,  in  the  adult,  from  ^  to 
•J-  inch.  The  first  layer  shows  delicate  nerve-fibrils  run- 


STRUCTURE   OF   THE   SPINAL   CORD   AND   BRAIN.       67 

ning  parallel  to  the  surface  and  interlacing  with  a  few 
small  branching  nerve-cells.  The  second  and  third  layers 
contain  a  large  number  of  pyramidal  or  spindle-shaped 
cells.  In  the  second  layer  the  cells  are  about  ^-^  inch  in 
diameter,  and  are  closely  pressed  together.  In  the  third 
are  fewer  cells,  but  they  increase  in  size  to  perhaps  y^Vo- 
or  -^  inch,  and  have  their  long  axes  perpendicular  to 
the  surface.  The  fourth  layer  contains  large  numbers  of 
small,  globular,  and  branching  cells ;  the  fifth,  spindle- 
shaped  bodies  with  long  tapering  processes,  and  smaller 
irregular  cells,  very  compactly  accumulated. 

The  number  of  nerve-cells  in  the  cortex  is  enormous. 
In  a  bit  of  its  substance,  1  millimeter  square  and  TV  milli- 
meter thick,  100  to  120  have,  on  an  average,  been  counted. 

Modifications  of  the  arrangement  just  described  are 
found  in  certain  regions  of  the  cerebral  cortex.  In  the 
occipital  lobe,  for  example,  the  number  of  layers  is  increased, 
by  intercalating  granule  layers,  to  seven  or  eight.  In  cer- 
tain layers,  called  "motor,"  large  cells  (named  by  Betz 
"  giant-cells  "  )  resembling  those  in  the  anterior  horns  of 
the  spinal  cord,  are  found.  Conjecture  and  research  are  at 
work  with  the  question,  whether  certain  of  these  layers, 
and  the  cells  they  contain,  are  not  more  distinctively  sen- 
sory, and  certain  others  more  distinctively  motor.  This 
subject  is  very  important  in  its  relations  to  our  entire 
conception  of  the  nature  and  functions  of  the  cerebral 
mechanism.  But  as  yet  histology,  even  when  aided  by 
physiological  experiment,  has  determined  nothing  definite. 

Systems  of  Cerebral  Nerve-fibres.  —  The  nerve-fibres  of  the 
white  substance  of  the  brain  are  of  three  classes,  according 
to  the  destination  of  the  fascicles  into  which  the  fibres  are 
gathered.  There  are  the  (1)  downgoing  or  peduncular, 
(2)  the  comrnissural,  and  (3)  the  arcuate  (fibrae  propriae). 
The  peduncular  system  of  nerve-fibres  connects  the  cere- 
brum with  the  lower  parts  of  the  encephalon.  This  system 


68  PHYSIOLOGICAL  PSYCHOLOGY. 

is  called  the  corona  radiata-,  it  is  the  "blossoming  out" 
of  the  nerve-fibres  on  their  way  between  the  hemispheres 
and  the  lower  ganglia.  Looked  at  from  above,  this  system 
represents  the  contracting  of  the  downgoing  nerve-tracts 
as  they  are  narrowed  into  the  internal  capsule  and  then 
taken  on  to  the  crura  cerebri.  (See  Fig.  27.)  A  con- 
siderable portion  of  this  system,  however,  terminates  in 
the  optic  thalami  and  the  striate  bodies. 

The  principal  tract  of  the  commissural  system  of  cerebral 
fibres  is  formed  in  the  corpus  callosum.  This  system  con- 
nects the  two  hemispheres  of  the  brain.  That  the  fibres 
of  the  corpus  callosum  are  not  wholly  commissural,  follows 
from  the  fact  that,  since  this  commissure  lies  above  the 
plane  of  the  corona  radiata,  the  peduncular  system,  on  its 
way  to  the  hemispheres,  here  intersects  with  the  commissu- 
ral. A  smaller  commissure  (the  anterior)  passes  below  the 
lenticular  nuclei  of  the  striate  bodies  and  connects  the  con- 
volutions around  the  Sylvian  fissure. 

The  system  of  arcuate  fibres  of  the  cerebrum  connects 
the  gray  matter  of  more  or  less  distant  convolutions  of  the 
same  hemisphere.  These  fibres  may  often  be  described  as 
a  "garland-like  interweaving  "  of  two  convolutions  around 
the  sulcus  between  them.  In  certain  localities,  where  the 
fascicles  into  which  the  fibres  are  gathered  are  strongly 
marked,  they  have  received  special  names ;  such  are  the 
fasciculus  uncinatus,  which  crosses  the  bottom  of  the 
Sylvian  fissure,  the  fillet  of  the  gyrus  fornicatus,  extending 
longitudinally  in  that  convolution,  etc.  The  function 
of  the  arcuate  fibres  is  plainly  that  of  joining  into  a 
diversified  unity  the  different  portions  of  each  cerebral 
hemisphere. 


STRUCTURE   OF   THE   SPINAL  CORD   AND   BRAIN.       69 


PATHS  OF  NERVOUS  IMPULSES   IN  THE   SPINAL  CORD  AND 

BRAIN. 

The  foregoing  brief  description  of  the  cerebro-spinal 
nervous  system  shows  that  it  is  a  mechanism  constructed 
so  as  to  afford  "  Tracts  "  or  "  Paths,"  to  a  greater  or  less 
degree  distinct,  for  the  transmission  of  nervous  impulses. 
It  is,  however,  only  to  a  very  limited  degree  that  histology 
alone,  or  even  when  helped  by  embryology  and  pathology, 
can  make  out  precisely  where  these  paths  lie.  (Several  of 
those  belonging  to  the  spinal  cord,  that  are  more  distinctly 
traceable  by  the  histological  method  —  for  example,  the 
pyramidal  tract,  both  crossed  and  uncrossed,  the  direct 
lateral  cerebellar  tract,  the  paths  of  the  anterior  and  of  the 
posterior  nerve-roots,  etc.  —  have  already  been  described.) 
In  the  brain  also  it  is  thought  by  eminent  authorities  that 
certain  chains  of  nervous  organs,  in  which  the  gray  masses 
are  successively  connected  by  nerve-cords  between,  can  be 
pointed  out.  With  this  in  view,  three  collections  of  nervous 
matter  (the  locus  niger,  and  the  two  nuclei  of  the  striate 
bodies),  with  the  bundles  of  nerve-fibres  which  bind  them 
together,  have  been  called  "ganglia  of  the  crusta"  by 
Meynert.  Another  chain,  consisting  of  the  tegmentum, 
the  red  nucleus  (a  collection  of  large  pigmented  cells  near 
the  Sylvian  Aqueduct),  the  corpora  geniculata,  and  the 
optic  thalami,  has  been  proposed  by  the  same  authority. 

It  is  only,  however,  when  the  aid  of  physiology  (patho- 
logical and  experimental)  is  summoned,  that  much  prog- 
ress toward  certainty  can  be  made  in  determining  paths 
of  nervous  impulse  within  the  cerebro-spinal  axis.  Even 
with  this  aid,  there  is  still  room  for  conjecture  and  uncer- 
tainty. Anticipating  additional  evidence  which  will  sub- 
sequently be  more  fully  described,  we  now  indicate  the 
probabilities  concerning  certain  of  these  paths. 

Paths  in  the  Boots  of  the  Spinal  Cord.  —  The  honor  of  the 


70  PHYSIOLOGICAL   PSYCHOLOGY. 

truly  "  epoch-making  "  discovery,  that  the  anterior  roots  of 
the  spinal  cord  are  motor  and  the  posterior,  sensory,  must 
be  divided  between  Sir  Charles  Bell  and  Magendie.  This 
discovery  may  be  said  to  have  opened  the  door  to  modern 
experimental  physiology.  The  demonstration  of  the  fact 
is  performed  by  dividing  these  roots,  respectively,  and  then 
observing  the  physiological  results.  When  a  posterior  root 
is  divided,  all  the  structures  supplied  by  the  divided  nerve 
lose  their  sensibility;  while  the  muscles  supplied  by  the 
corresponding  anterior  root  continue  to  be  thrown  into 
action  by  the  will  and  by  reflex  stimulation.  In  this  case 
also,  stimulation  of  the  central  end  of  the  divided  root 
produces  sensory  effects ;  but  stimulation  of  the  peripheral 
end  produces  no  motion.  When  an  anterior  root  is  divided, 
on  the  contrary,  the  muscles  supplied  by  the  nerves  of  this 
root  cannot  be  made  to  act  by  will ;  but  no  sensory  paraly- 
sis is  produced.  Moreover,  stimulation  of  the  peripheral 
end  of  the  nerve  will  now  throw  the  muscles  into  contrac- 
tion ;  but  stimulation  of  the  central  end  will  produce  no 
effects.  Thus  far,  then,  the  paths  in  the  spinal  cord  may 
be  said  to  be  distinctly  traceable. 

Paths  in  the  Anterior  Columns  of  the  Cord.  —  The  general 
arrangement  of  the  motor  paths  in  the  anterior  part  of  the 
spinal  cord  is  maintained  throughout.  Histology  has 
shown  us,  however  (p.  40),  that  the  two  halves  of  the 
cord  are  bound  together  by  the  commissures  ;  this  fact  sug- 
gests a  crossing,  at  least  partial,  from  one  side  to  the  other, 
of  the  nervous  impulses.  Experiment  upon  the  lower 
animals  seems  to  show  that  a  partial  crossing  of  the  motor 
paths  takes  place  in  the  cord.  In  man's  case,  most  if 
not  all  of  this  crossing  from  side  to  side,  so  far  as  the 
paths  of  voluntary  motion  are  concerned,  occurs  very  high- 
up,  if  at  all,  in  the  spinal  cord.  But  the  structure  of  this 
organ  is  such  as  plainly  to  provide  for  an  intermingling 
of  the  paths  of  the  sensory  and  the  motor  roots  at  about 


STRUCTURE   OF  THE   SPINAL   CORD   AND   BRAIN.        71 

the  same  level.  Thus  its  character  as  a  pile  of  centres  is 
maintained. 

Paths  in  the  Posterior  Columns  of  the  Cord.  —  In  the 
posterior  parts  of  the  spinal  cord  are  the  paths  by  which 
the  sensory  impulses  chiefly  run  from  the  posterior  roots 
up  to  the  brain.  These  paths  also  seem  to  undergo  a  par- 
tial crossing  from  one  side  to  the  other  in  the  cord.  In 
the  lower  animals,  according  to  the  evidence  of  experiment, 
the  sense  of  feeling  is  retained  after  the  cord  has  been  cut 
entirely  through  from  the  front  to  the  posterior  columns. 
Stimulation  of  these  columns  produces  signs  of  pain  and 
other  sensory  effects.  Some  investigators  would  confine 
the  paths,  by  which  sensory  impulses  of  touch  pass  along 
the  cord,  to  the  posterior  columns ;  they  would  assign 
to  the  gray  matter  of  the  cord,  the  paths  for  impulses  giving 
rise  to  sensations  of  pain.  Others  consider  that  these 
columns  conduct  sensory  impulses  only  so  far  as  the  nerves 
from  the  sensory  roots  pass  through  them ;  it  is  then  the 
gray  substance  which  carries  these  impulses  upward.  The 
conclusions  by  which  some  experimenters  locate  motor,  and 
even  voluntary  motor,  paths  in  the  posterior  columns,  are 
extremely  doubtful. 

Paths  in  the  Lateral  Columns  of  the  Cord,  —  In  these  por- 
tions of  the  spinal  cord  both  the  paths  of  motor  and  those 
of  sensory  impulses  are  found.  As  to  the  former  there  is 
little  or  no  dispute.  As  to  the  existence  of  sensory  paths 
in  the  lateral  portions  of  the  cord,  the  evidence  of  experi- 
ment is  somewhat  conflicting ;  but,  on  the  whole,  it  seems 
to  favor  an  affirmative  conclusion.  This  conclusion  accords 
well  with  histology. 

It  must  be  remembered  that,  when  we  speak  of  "  paths 
in  the  spinal  cord,"  we  are  not  to  think  of  a  perfectly  fixed 
and  rigid  course  like  that  of  the  iron  rails  upon  which  a 
locomotive  runs.  No  nerve-commotion,  when  started  in  any 
portion  of  the  cord,  is  necessarily  and  under  all  circum- 


72  PHYSIOLOGICAL  PSYCHOLOGY. 

stances  compelled  to  take  one,  and  only  one,  path  to  its 
destination.  Secondary  paths,  besides  the  primary  and 
more  ordinary  paths,  exist  in  abundance.  A  considerable 
work  of  substitution,  especially  as  regards  the  tracts  along 
which  the  sensory  impulses  move,  may  then  take  place. 
Even  in  the  case  of  the  voluntary  motor  tracts  in  man, 
although  such  a  work  of  "  substitution  "  apparently  does 
not  take  place,  a  certain  latitude  of  movement  from  a 
straightforward  course  undoubtedly  exists. 

Paths  in  the  Brain.  —  The  evidence  already  presented 
from  histology  indicates  that  certain  tracts,  probably  motor, 
pass  from  the  crusta  through  the  internal  capsule,  without 
entering  the  basal  ganglia,  into  the  frontal  and  parietal  — 
convolutions.     Other  tracts,  which  are  probably  sensory, 
run  through  the  tegmentum,  enter  the  thalamus  and  sub-  < 
thalamic  region ;  then,  after  being  redistributed,  emerge  to 
find  their  way  to  the  temporal  and  occipital  lobes.     How 
well  physiological   experiment   agrees  with   this   general 
conclusion,  we  shall  see  subsequently. 

The  paths  by  which  the  sensory  impulses  travel  in  the 
brain  must  be  exceedingly  intricate ;  for  the  phenomena 
connected  with  all  sensory  disturbances  are  very  compli- 
cated and  often  conflicting.  For  example,  if  a  sensory 
cranial  nerve  is  severed,  the  different  functions  of  feeling 
pain,  of  pressure,  and  of  temperature,  and  the  power  of 
localization,  in  the  region  supplied  by  that  nerve,  are  all 
lost.  But  disease  of  the  cerebro-spinal  axis  may  impair 
one  or  more  of  these  functions,  and  leave  the  other  intact. 
Again,  loss  of  the  sense  of  temperature  and  of  the  mus- 
cular sense  rarely  occur  separately;  but  muscular  sense 
frequently  disappears  and  the  sensitiveness  of  the  skin  to 
pressure  is  retained. 

The  paths  both  of  motor  and  of  sensory  impulses,  cross 
in  the  region  of  the  pons  Varolii  and  medulla  oblongata. 
All  the  paths  of  both  kinds  lie  very  close  to  each  other  in 


STRUCTURE   OF  THE   SPINAL   CORD   AND   BRAIN.       73 

the  white  nervous  substance  surrounding  the  basal  gan- 
glia. There  is  considerable  recent  evidence  1  to  show  that 
the  tracts  followed  by  impulses  of  muscular  sensation  pass 
through  the  posterior  columns  or  cornua  of  the  spinal 
cord,  and  are  gathered  into  more  or  less  distinct  bundles, 
at  the  back  part  of  the  internal  capsule,  before  they  diverge 
to  enter  the  hemispheres. 

The  confidence  with  which  M.  Luys,  in  his  work  on  the 
"  Brain  and  its  Functions,"  has  localized  the  paths  of 
motor  impulses  wholly  in  the  striate  bodies,  and  those  of 
the  different  sensory  impulses,  olfactory,  visual,  tactual, 
auditory,  in  those  four  centres  of  the  optic  thalami  which 
he  distinguishes,  cannot  be  maintained.  The  tendency  of 
modern  investigation  is  to  place  more  emphasis  upon  the 
fibrous  nerve-matter  surrounding  these  organs  as  furnish- 
ing paths  for  the  conduction  of  both  kinds  of  impulses. 

Substantially,  in  its  more  obvious  outlines,  as  we  have 
described  it,  but  wTith  an  infinite  and  indescribable  com- 
plexity of  details,  is  constructed  this  marvellous  mechan- 
ism of  the  nervous  system.  Some  of  the  more  particular 
functions  of  its  parts  will  be  investigated  in  other  con- 
nections. But  even  this  description  shows  its  fitness  to 
serve  as  a  physical  basis  for  the  equally  indefinite  and 
indescribable  complexity  of  the  mental  life.  How  many 
variations  of  fundamental  types  do  the  organs  of  the  phys- 
ical mechanism  display !  And  of  how  many  kinds,  shades, 
degrees  of  intensity,  and  modes  of  local  coloring,  are  our 
sensations  and  their  representative  images  susceptible ! 
The  immense  variety  and  essential  unity  of  this  physical 
basis  suggest  a  corresponding  variety  in  unity  of  the 
psychical  life. 

1  Bastian,  in  Brain,  April,  1887,  p.  69  f. 


CHAPTER  III. 

STRUCTURE   OF   THE   ORGANS   OF  SENSE  AND 
MOTION. 

IN  the  general  division  of  labor  among  the  organs  of 
the  nervous  system,  certain  groups  of  cells  at  the  surface 
of  the  body  become  especially  sensitive  to  external  stimuli. 
These  cells  accordingly  acquire  the  special  function  of 
receiving  and  modifying  the  action  of  such  stimuli,  and 
thus  of  setting  up  in  the  conducting  nerves  a  neural  pro- 
cess which  is  propagated  to  the  central  organs.  Every 
"  end-organ,"  therefore,  looks  both  inward  and  outward. 

Significance  and  Kinds  of  End-organs.  —  The  end-organs 
are  divided  into  two  classes :  first,  end-organs  of  sense, 
and  second,  end-organs  of  motion.  The  former  are  in 
general  made  up  of  cells,  which,  posteriorly,  pass  into 
nerve-threads  that  are  gathered  into  the  nerve  of  special 
sense ;  and  which,  anteriorly,  develop  conical  or  fusiform 
processes.  The  simplest  type  is,  then,  a  hair-like  process 
extending  outward  and  connected  by  a  sensitive  cell  with 
a  nervous  filament  extending  inward.  Only  a  small  part, 
however,  of  what  are  called  "the  organs  of  the  special 
senses  "  belongs  to  the  nervous  system.  The  greater  part 
(as,  for  example,  of  the  ear,  the  eye,  the  skin)  consists 
of  mechanical  contrivances  designed  to  modify  the  exter- 
nal stimulus,  while  conducting  it  to  the  truly  nervous 
mechanism. 

End-organs  of  Smell.  —  That  portion  of  the  mucous  mem- 
brane of  the  nose  which  clothes  the  upper  region  of  the 
nasal  cavity,  and  is  called  regio  olfactoria,  contains  the 
74 


ORGANS   OF   SENSE  AND  MOTION. 


75 


end-organs  of   smell.     Two  different   kinds  of   cells   are 

here  discovered.     By  Max  Schultze  and  most 

other   investigators,   one   of   these  is  consid- 

ered  non-nervous    and    epithelial,   the   other 

nervous   and   olfactory.      The  epithelial  cells 

are  the  larger,  have  an  oval  nucleus  of  consid- 

erable size,  and  extend  through  the  whole  epi- 

thelial layer.     The  olfactory  cells  are  spindle- 

shaped,  with  a  round  nucleus,  and  very  fine 

long  processes.      Other  investigators  believe 

that  this  difference  is  not  a  fixed  distinction 

of  kinds,  but  is  rather  indicative  of  different 

stages  of  development.     The  exact  relation  of 

the  fibrils  of  the  olfactory  nerve  (which  is  the 

specific  nerve  of  smell,  and  really,  in  part,  a 

lobe  of  the  brain)  to  the  epithelium  of  this 

region  is  not  made  out,     It  seems  probable, 

however,  that  they  do  not  pass  directly  into 

J  J 

the  processes  of  the  end-organ  cells,  but  are 
lost  in  a  network  whose  interstices  are  filled 
up  with  nerve-granules. 

The  contrivance  for  bringing  the  stimulus  to  the  end- 
organs  of  smell  is  comparatively  simple.  It  is  necessary 
only  that  a  current  of  air,  in  which  the  stimulating  parti- 
cles float,  should  be  drawn  over  the  mucous  membrane  of 
the  region.  Since  in  expiration  the  current  is  carried  past 
the  sensory  parts  without  striking  them,  smelling  is  almost 
entirely  confined  to  inspiration.  When  "snuffing,"  we 
increase  the  amount  and  force  of  the  air  drawn  into  this 
region,  by  first  creating  a  partial  vacuum  in  its  cavity. 

End-organs  of  Taste.  —  On  the  upper  surface  of  the  root, 
and  on  the  borders  and  apex  of  the  tongue,  and  in  some 
cases,  on  the  anterior  portion  of  the  soft  palate,  are  found 
certain  papillae.  Of  those  papillae  which  contain  the  end- 
organs  of  taste  two  kinds  are  distinguished  ;  the  circumval- 


FIG.  32.  —  Oi- 
Eplthelial    Cefls 


Af 


76 


PHYSIOLOGICAL   PSYCHOLOGY. 


FIG.  33.  —  Transverse  Section  through  a  Pap- 
illa Circumvallata  of  a  Calf.  Showing  the  ar- 
rangement and  distribution  of  the  gustatory  bulb. 
M/t.  (Engelmann.) 


latce  and  the  fungiformes.  The  circumvallate  papillae  are 
composed  of  connective  tissue  invested  by  epithelium 
arranged  in  plates  (laminae).  At  the  sides  where  the 
epithelial  layer  is  thinner,  the  end-organs  of  taste  form 

a  zone  which  extends  up- 
ward to  the  level  where 
the  papillae  are  no  longer 
protected  by  the  lateral 
wall.  In  the  fungiform 
papillae  these  organs  ap- 
pear in  the  epithelium 
which  covers  their  upper 
surface,  and  in  the  sur- 
faces of  the  sides. 
The  Gustatory  Flasks.  —  These  structures,  sometimes 
called  "  gustatory  knobs  "  or  "  bulbs  "  occupy  flask-shaped 
cavities  in  the  papillae,  which  they  completely  fill.  Their 
lower  part  rests  on  connective  tissue ;  their  upper  part  or 
neck  has  an  opening  or  pore,  of  from  ^oir  to  rAr  inch  in 
diameter.  Each  flask  consists  of  from  fifteen  to  thirty 

long,  thin  cells,  ar- 
ranged like  the  leaves 
of  a  bud  around  its 
axis.  The  margin  of 
the  pore  is  formed  by 
bringing  several  cells 
together. 

The  gustatory  flasks 
also   are   composed  of 

FIG.  34.  —  Gustatory  Bulbs  from  the  Lateral  Gus-     tWO  kinds  of  Cells,  OU6 
tatory  Organ  of  the  Rabbit,    «A.     (Engelmann.)         ^^  the  QfaQT  gu8_ 

tatory.  The  epithelial  or  "  investing  "  cells  are  long,  nar- 
row, bent,  spindle-shaped,  with  a  nucleus  well  marked. 
The  outward  end  is  pointed,  the  central  end  branching. 
The  gustatory  cells  are  thin,  long,  and  highly  refractive  of 


ORGANS   OF   SENSE   AND   MOTION. 


77 


light,  with  nearly  the  whole  body  occupied  by  an  elliptical 
nucleus.  The  body  of  the  cell  is  elongated  into  two  pro- 
cesses ;  the  upper  one  of  which  is  broad,  but  bears  a  short, 
tine  point,  like  a  stiff 
hair.  This  point  lies 
in  a  canal  and  rarely 
projects  from  the 
pore  of  the  flask. 

The  glosso-pha- 
ryngeal  nerve  is  the 
principal  nerve  of 
taste ;  but  the  lingual 

.  FIG.  35.  —  a,  Isolated  Gustatory  Cells,  from  the  Lat- 

braiicll  OI    the    trigfe-  eral  Organ  of  the  Rabbit;  b,  an  Investing  and  Two  GKis- 

_  .      °  tatory  Cells,  isolated  but  still  in  connection.    «>%.    (En- 

mmUS  IS  thought  by  gelmann.) 

some  to  take  part  in  sensations  of  this  sense.  The  nerve 
is  distributed  to  the  back  of  the  tongue,  then  enters 
the  papillae  where  it  forms  a 
minute  plexus  interspersed  with 
nerve-granules.  Its  connection 
with  the  nerve-cells  of  sense  is 
probably  indirect,  through  this 
plexus  and  its  granules. 

End-organs  of  Touch.  —  The 
sensory  nerves  distributed  to 
the  skin,  the  organ  of  touch  in 
the  larger  sense  of  the  word, 
terminate  either  in  free  end- 
fibrils  or  in  special  structures 
called  "  tactile  corpuscles "  or 
"  end-bulbs."  These  special 
structures  have  been  named 
after  different  investigators. 
The  three  or  four  different  kinds 
may,  however,  be  considered 
as  modifications  of  one  type.  The  first  of  these  structures 


FIG.  36.  —  Corpuscle  of  Pacini  (or 
Vater)  from  the  Mesentery  of  the  Cat. 
( After  Frey.)  a, nerve  with  its  sheaths; 
b,  system  of  tunics  constituting  the 
capsule  of  the  corpuscle ;  c,  axial  canal, 
in  which  the  nerve-fibre  ends. 


78 


PHYSIOLOGICAL  PSYCHOLOGY. 


FIG.  37.  —  End-bulbs  from 
the  Conjunctiva  of  the  Human 
Eye.  (After  Kolliker.)  1, 
has  two  nerve-fibres  which 
form  a  coil  within  the  end- 
bulb;  2,  has  a  fatty  core. 
The  nerve-fibre  of  5  ends 
within  in  the  form  of  a  knot. 


to  be  discovered  (more  than  a  hundred  and  fifty  years 
since,  by  Vater)  was  the  so-called  "  Corpuscle  of  Pacini " 
(or  Vater).  These  bodies  consist  of 
layers  of  connective  tissue,  arranged 
concentrically,  and  most  closely 
packed  near  the  centre.  The  layers 
surround  a  cavity  containing  a  soft, 
nucleated  material  into  which  the 
nerve  penetrates.  The  axis-cylinder 
of  the  nerve-fibre  which  enters  the 
bulb  is  finely  fibrillated.  The  bulb 
consists  of  granular  substance.  In 
man  these  bodies  abound  in  the  palms 
of  the  hand  and  the  soles  of  the  feet ; 
but  especially  in  the  palmar  surfaces  of  the  fingers  and 
toes.  In  some  places  they  are  visible  to  the  naked  eye 

as  a  minute  grain  ^  to  £  inch 
in  diameter. 

The  "End-bulbs  of  Krause" 
are  similar  to  the  foregoing 
structures.  They  are  small 
capsules  of  connective  tissue 
in  which  nuclei  can  be  de- 
tected, and  in  which  the  nerve- 
fibrils  seem  to  terminate  in  a 
coiled  mass  or  bulbous  ex- 
tremity. 

The  "  Corpuscles  of  Wag- 
ner" (or  Meissner)  are  oval- 
shaped  bodies  bearing  some 
resemblance  to  a  miniature  fir- 
cone. The  nerve-fibres  appear 
like  "  creeping  roots,"  to  wind 
beneath  the  papillae  of  the  skin  and,  interpenetrating 
them  here  and  there,  to  terminate  in  the  corpuscles.  Within 


FIG.  38.  — Corpuscles  of  Touch.  (Af- 
ter Frey.)  a,  from  the  soft  skin  of  the 
duck's  bill;  6  and  c,  from  the  papillae  of 
the  tongue  of  the  same  animal. 


ORGANS   OF   SENSE   AND   MOTION.  79 

the  corpuscles,  the  fibrils  are  described  as  forming  two  or 
three  coils  and  joining  together  in  loops.  Of  400  papillae 
counted  in  ^  inch  square,  on  the  third  phalanx  of  the 
index  finger,  these  corpuscles  were  discovered  in  108. 
They  are  from  -^  to  y^j-  inch  long. 

Since  the  surface  of  the  skin  is  everywhere  sensitive  to 
pressure  and  to  temperature,  but  these  special  structures 
are  not  found  everywhere,  it  follows  that  they  cannot  be 
the  sole  organs  of  touch.  As  has  already  been  said,  the 
free  nerve-fibrils  must  act  as  the  end-organs  of  those  sen- 
sations which  belong  to  the  whole  surface  of  the  body. 
Research  and  conjecture  have  not  yet  succeeded  in  assign- 
ing special  functions  to  any  of  the  varieties  of  the  end- 
organs  of  touch. 

STRUCTURE  OF  THE  EYE. 

With  the  exception  of  the  ear,  the  end-organ  for  the 
sensations  of  light  and  color  is  by  far  the  most  elaborate 
and  complicated.  It  is  obviously  adapted  to  be  the  instru- 
ment of  an  intellectual  and  "  geometrical "  sense.  Con- 
sidered as  a  whole,  its  plan  may  be  stated  in  one  sentence 
as  follows:  The  Eye  is  an  optical  instrument  of  the 
nature  of  a  water  camera  obscura,  with  a  self-adjusting 
lens,  and  a  concave  sensitive  membrane  of  nervous  matter, 
on  which  an  image  is  formed.  Its  structure  affords  a 
practical  solution  of  several  problems.  Among  these  the 
first  is  of  a  purely  mechanical  sort,  and  may  be  called  "  the 
problem  of  protection." 

Coats  or  Tunics  of  the  Eyeball.  —  Three  coverings  sur- 
round the  eye,  one  of  which,  in  part,  acts  also  as  a  refract- 
ing medium.  (1)  The  external  coat  consists  of  two  parts, 
(a)  the  Sclerotic  (or  "  white  of  the  eye  ")  a  firm,  fibrous 
membrane  of  connective  tissue  intermingled  with  elastic 
fibres ;  and  (6)  the  Cornea,  or  translucent  front  one-sixth 
part,  which  rises  and  bulges  in  the  middle  like  a  watch- 


80 


PHYSIOLOGICAL  PSYCHOLOGY. 


glass,  and  which  is  covered  with  conjunctiva!  epithelium. 
(2)  The  second  coat  also  consists  of  two  parts,  (a)  the 
Choroid,  which  is  of  a  dark  brown  color,  due  to  the  pres- 


FIG.  39.  — Horizontal  Section  through  the  Left  Eye.  4/i-  (Schematic,  from  G/egenbaur.) 

ence  of  pigment  cells ;  and  (6)  the  Iris,  a  circular,  disk- 
shaped  diaphragm,  in  the  form  of  a  lens,  which  is  bathed 
with  aqueous  humor  and  has  in  its  centre  a  circular  aper- 
ture (the  "pupil").  The  anterior  border  around  the  iris 
consists  of  the  ciliary  muscle  and  the  ciliary  processes. 


ORGANS   OF   SENSE   AND  MOTION.  81 

(3)  The  Retina  is  the  third,  or  inner  coat  of  the  eye.  It 
is  a  delicate  membrane,  consisting  of  nine  or  ten  layers, 
of  exquisite  transparency  and  almost  perfect  optical  homo- 
geneity. Its  inner  surface  is  moulded  on  the  vitreous 
body,  and  it  extends  from  the  entrance  of  the  optic  nerve 
nearly  as  far  forward  as  the  ciliary  processes. 

Refracting  Media  of  the  Eye.  —  The  eye  has  four  translu- 
cent refracting  media.  These  are  (1)  the  Cornea,  already 
spoken  of  as  the  anterior  one-sixth  of  the  outer  tunic  of 
the  eye.  (2)  The  Aqueous  Humor  fills  the  space  back  of 
the  cornea  and  is  divided  by  the  iris  into  two  chambers,  of" 
which  the  front  one  is  the  larger.  It  is  limpid  and  watery, 
but  holds  certain  salts  in  solution.  (3)  The  Crystalline 
Lens  is  situated  between  the  iris  and  the  vitreous  body.  It 
is  transparent,  biconvex,  with  its  antero-posterior  diameter 
about  one-third  less  than  the  transverse  diameter.  It  con- 
sists of  a  capsule  and  an  enclosed  body,  is  of  "buttery 
consistency"  and  made  up,  like  an  onion,  of  concentric 
layers.  (4)  The  Vitreous  Humor  consists  of  a  number  of 
firm  sheets,  between  which  fluid  is  contained,  built  into  a 
body  that  is,  optically  considered,  transparent  and  nearly 
homogeneous.  It  is  a  gelatinous  form  of  connective  tis- 
sue. Though  it  occupies  most  of  the  bulk  of  the  eyeball, 
it  has  comparatively  little  physiological  significance. 

Appendages  of  the  Eyeball.  —  Of  the  accessory  parts  of 
the  eye, — eyebrows,  eyelids,  lachrymal  glands,  etc.,  —  only 
the  muscles  have  any  interest  to  physiological  psychology. 
Of  these  there  are  six  which  are  attached  to  the  eyeball, 
somewhat  like  a  bridle  to  a  horse's  head.  Four  of  these 
muscles  spring  from  the  bony  wall  near  the  point  where 
the  optic  nerve  enters,  extend  through  the  length  of  the 
socket,  and  pass  directly  to  the  eyeball,  where  they  are 
attached  to  it,  —  one  above,  one  below,  one  on  the  outer, 
and  one  on  the  inner  side  (the  recti  ;  internal  and  external, 
superior  and  inferior).  The  other  two  muscles  of  the  eye 


82  PHYSIOLOGICAL   PSYCHOLOGY. 

are  called  oblique.  The  superior  internal  oblique,  instead 
of  running  directly  to  connect  with  the  eyeball,  passes 
through  a  ring,  then  turns  round,  and  is  attached  obliquely 


FIG.  40.  —Muscles  of  the  Left  Human         FIG.  41.  —  Muscles  of  the  Left  Human  Eye, 

Eye,  seen  from  above,    rs,  rectus  supe-  seen  from  the  outside.    Ir,  levator  of  the  upper 

rior;  re,  rectus  externus;  and  rit,  rectus  eyelid,  which  covers  the  rectus  superior,  n; 

internus;  os,  superior  oblique,  with  its  re,  os,  as  in  the  preceding  figure;   rif,  rectus 

tendon  t,  which  runs  through  the  mem-  inferior;  oi,  inferior  oblique, 
branous  pulley  «,  at  the  inner  wall  of 
the  cavity  of  the  eyeball. 

to  the  upper  surface.  The  other  oblique  muscle  begins  at 
the  inner  wall  in  the  socket,  passes  under  the  eyeball,  and 
is  attached  to  it  opposite  to  the  superior  oblique  muscle. 

Formation  of  the  Retinal  Image.  —  The  problem  which  is 
to  be  solved  by  the  end-organ  of  vision,  in  its  most  general 
form,  may  be  stated  as  follows :  A  mosaic  of  localized  sen- 
sations of  light  and  color  must  be  so  constructed  that  changes 
in  the  quantity,  quality,  local  coloring,  and  sequence  of  these 
sensations  shall  be  interpreted  as  the  size,  shape,  locality,  and 
motion  of  external  visible  objects.  The  most  important  part 
of  the  solution  of  this  general  problem  falls  upon  the 
retina.  And  the  most  important  problem,  subordinate  to 
the  general  problem,  is  the  "  formation  of  an  image  "  upon 
the  retina.  But  this  problem  is  an  optical  one.  It  is  solved 
by  the  translucent  refracting  media  of  the  eye. 

The  four  media  of  the  eye  constitute  a  system  of  refract- 


ORGANS   OF  SENSE  AND  MOTION. 


83 


ing  surfaces,  each  of  which  is  separated  from  the  one  adjoin- 
ing by  a  circular  cut,  as  it  were,  in  the  whole  refracting 
substance.  Thus  the  "image"  of  the  first  refracting  sur- 
face of  this  system  of  surfaces  becomes  an  "  object,"  as  it 
were,  for  the  second  refracting  surface ;  the  second  "  image  " 
an  "  object "  for  the  third  surface,  and  so  on.  In  tracing 
the  course  of  the  rays  through  these  media  two  things 
must  chiefly  be  taken  into  the  account.  They  are  (1)  the 
indices  of  the  refraction  of  the  refracting  media,  and  (2) 
the  geometrical  form  and  position  of  all  the  limiting 
surfaces. 

Our  knowledge  of  the  indices  of  the  refracting  media 
of  the  eye  is  derived  by  taking  the  average  result  of  an 
examination  of  a  number  of  eyes  supposed  to  be  normal. 
In  this  calculation  the  lens  is,  of  course,  much  the  most 
important  of  all  the  media.  But  the  structure  of  the  lens 
is  such  (see  Fig.  42)  that  the  index  of  refraction  is  not 


FIG.  42.  —  Median  Section  through  the  Axis  of  the  Lens  of  the  Eye.   (Schematic,  after 
Babuchin.) 

homogeneous  throughout.  Each  layer  has  its  own  index, 
and  the  amount  of  the  index  of  each  layer  increases  toward 
the  kernel  of  the  lens.  By  this  contrivance  the  entire 
work  of  refraction  done  by  the  lens  is  made  greater  than 
the  work  which  could  be  done  by  a  homogeneous  lens  with 
an  index  of  refraction  equal  to  that  of  its  most  highly 


84  PHYSIOLOGICAL  PSYCHOLOGY. 

refracting  part.  The  mean  index  for  the  lens  of  the 
normal  eye  may  be  given  =  1.4545.  The  mean  index  of 
refraction  for  the  cornea  is  given  at  about  1.3507 ;  of  the 
aqueous  humor  at  1.3365-1.3420 ;  of  the  vitreous  body 
at  1.3382-1.3485. 

The  position  and  form  of  the  surfaces  of  the  refracting 
media  can  be  only  approximately  determined.  Three  of 
these  surfaces  are  most  important,  — namely,  the  anterior  of 
the  cornea  and  the  two  surfaces  of  the  lens.  The  convexity 
of  the  anterior  surface  of  the  cornea  is  greater  toward  its 
edge  than  at  its  vertex,  where  it  resembles  a  section  o'  an 
ellipsoid.  The  images  formed  when  the  pupil  is  expanded 
are  thus  made  sharper.  No  observable  refraction  takes 
place  at  the  back  surface  of  the  cornea. 

Accommodation  of  the  Eye.  —  The  ability  to  alter  the  re- 
fracting conditions  of  the  eye  for  varying  distances  of  the 
object  is  called  its  "power  of  accommodation."  This 
adjustment  obviously  cannot  take  place  like  that  of  the 
photographer's  camera  obscura,  where  a  considerable  change 
can  be  made  in  the  distance  of  the  lens  from  the  screen  on 
which  the  image  is  formed.  It  is,  in  fact,  effected  by 
changing  the  convexity  of  the  lens,  —  principally,  if  not 
wholly,  at  its  anterior  surface.  This  may  be  demonstrated  by 
several  methods  of  experiment.  Indeed,  when  accommo- 
dation is  taking  place,  the  pupil  may  be  seen  to  contract 
and  to  draw  its  edge  forward.  Helmholtz  calculated  the 
amount  of  this  movement  at  TV  to  -fa  of  an  inch. 

The  mechanism  for  accommodation  of  the  eye  to  varying 
distances  of  the  objects  must  be  in  control  of  the  brain,  for 
the  accommodation  is  voluntary ;  it  must  also  consist  of 
muscles  that  lie  within  the  eyeball.  The  most  generally 
accepted  hypothesis  of  its  action  has  hitherto  been  that 
proposed  by  Helmholtz.  It  is  assumed  that  the  lens,  when 
at  rest,  is  in  a  state  of  tension  by  its  own  elastic  power. 
It  is  kept  flattened  by  the  radial  tension  of  the  suspensory 


ORGANS   OF   SENSE  AND   MOTION.  85 

ligament  (sometimes  called  the  zonula,  —  a  structureless 
membranous  body,  interposed  between  the  ciliary  part  of 
the  retina  and  the  vitreous  humor,  and  radiating  outward). 
The  mechanism  for  withdrawing  the  tension  consists  of  the 


Conjunctiva. 

c'prncac 


Can.  Scmewmii 


Proc.  ciliaris 


radiarer  circulurcr 

CiliarmttsTcel 

FIG.  43.  Sectional  View  of  the  Connections  of  the  Cornea,  Ciliary  Muscle,  Ciliary 
Processes,  etc.  10/i-  (Gegenbaur.) 

ciliary  muscle,  the  fibres  of  which  are  fixed  at  one  end,  at 
the  edge  of  the  cornea.  When  this  muscle  contracts,  the 
other  ends  of  the  fibres  are  drawn  toward  its  fixed  ends ; 
they  thus  relax  the  tension  of  the  suspensory  ligament  by 
pulling  in  the  opposite  direction  to  this  tension,  and  the 
lens  is  allowed  to  bulge  out  by  its  own  elastic  forces. 

More  recent  researches,  however,  seem  to  emphasize  the 
elasticity  of  the  vitreous  body  as  an  important  factor  in 
accommodation.  For  near  distances,  the  contraction  of  the 
circular  fibres  of  the  ciliary  body  increases  the  pressure  in 
the  vitreous  body,  driving  it  into  the  spaces  at  the  side 
of  the  lens,  and  bringing  the  suspensory  ligament  into  a 
stronger  convexity. 

It  is  the  oculo-motor  nerve  which  furnishes  in  the  poste- 
rior strands  of  its  roots,  the  fibres  that  serve  the  ciliary 
muscle.  Their  place  of  origin  is  in  the  back  part  of  the 


86 


PHYSIOLOGICAL  PSYCHOLOGY. 


floor  of  the  third  ventricle.  This  place  lies  very  close  to 
that  where  stimulation  produces  contraction  of  the  inter- 
nal rectus  muscle,  the  use  of  which  is  connected  with 
adjustment  for  near  distances.  Thus  all  the  mechanism  of 
accommodation  is  made  to  work  together  for  the  production 
of  the  image  on  the  retina.  [It  is  assumed  that  the  laws  of 
optics  under  which  the  formation  of  the  image  takes  place 
are  known,  or  are  to  be  acquired,  from  the  proper  sources.] 


Outer  surface. 


to  — Layer  of  pigment  cells. 

9  —  Layer  of  rods  and  cones. 
a Membrana  limitans  externa. 

7  — Outer  nuclear  layer. 
f    —  O uter  molecular  layer. 
Inner  nuclear  layer. 


Inner  molecular  layer. 


.  Layer  of  nerve-cells. 

*  — Layer  of  nerve-fibres. 

Membrana  limitans  in terna. 

Inner  surface. 
Fie.  44.  —  Diagrammatic  Section  of  the  Human  Retina.    (Schultze.) 


ORGANS    OF    SENSE   AND   MOTION. 


87 


r 


Given  the  formation  of  the  image 
upon  the  retina,  it  is  further  re- 
quired, in  order  .  to  vision,  that 
the  proper  physiological  processes 
should  be  set  up  within  this  organ. 
For  it  is  the  Retina  which  contains 
the  nervous  elements  by  whose  ac- 
tion the  system  of  refracted  rays 
is  changed  into  a  mosaic  of  nerve- 
commotions.  We  require  then  a 
detailed  description  of  the  struc- 
ture of  this  wonderful  organ. 

Layers  of  the  Retina.  —  The  ner- 
vous and  other  elements  of  the 
retina  are  arranged  in  ten  layers, 
—  counting  from  within  outward 
and  backward,  —  the  names  and 
order  of  which  are  given  in  the 
accompanying  schematic  represen- 
tation (see  Fig.  44y  By  no  means 
all  the  retinal  substance  is  nervous. 
Numerous  radial  fibres,  which  pene- 
trate its  entire  thickness,  are  of 
connective  tissue,  in  the  gaps  of 
which  the  true  nervous  elements 
lie  embedded.  These  gaps  are 
particularly  large  in  the  second, 
third,  fifth,  and  seventh  layers. 

Figure  45  shows  (diagrammati- 
cally)  the  connections  of  the 
true  nervous  elements  as  they 
extend  through  the  retinal  layers. 
We  notice  here  (a)  the  retinal 
fibres  of  the  optic  nerve,  lying 
parallel  to  the  surface.  They  are 


FIG.  45.  —  Diagrammatic  representation  of  the  Connections  of  the  Nerve-fibres  in  the 
Retina.     (Schultze.)     The  numbers  have  the  same  reference  as  in  Fig.  44. 


88 


PHYSIOLOGICAL   PSYCHOLOGY. 


non-medullated,  extremely  fine,  arranged  in  ray-like  bun- 
dles, radiating  on  all  sides  from  the  place  of  entrance  of 

the  nerve.  Next  (6)  come 
the  ganglion-cells,  resembling 
the  multipolar  nerve-corpus- 
cles of  the  rest  of  the  cerebro- 
spinal  system,  which  form  the 
principal  part  of  layer  No.  3. 
These  cells  at 
the  "yellow 
spot"  are  eight 
or  ten  deep,  but 
diminish  in 
number  toward 

FIG.    46. -Diagrammatic  Section   of  the  OTa  SCTTata. 

the  Posterior  Part  of  the  Retina  of  a  Pig.  /   \       TVio       T^QT. 

•«%.      (Schultze.)     7,  part  of  outer  nu-  \^J 
clear  layer;    8,   membrana   limitans   ex-  olomoTife 

terna;   9,  rods  and  cones.     Each  of  the  VOUb 
cones,  which  are  in  very  close  apposition,       *    lavpr    ATn     A 

contains  in  its  inner  segment  a  highly  re-  Ol    Itiyei    1>O.    ^ 

unkcnoewn°dy'  *  "  probably     con- 

sist of  extremely  fine  filaments  connected 
with  the  processes  of  the  ganglion-cells. 
(d)  Each  nucleus-like  body  in  No.  5  is 
thought  to  be  connected  by  fibres,  both  in- 
ward and  outward,  (e)  In  the  outer  molec- 
ular layer  (No.  6)  are  numerous  filaments 
of  nervous  character,  while  its  star-shaped 
cells  are  probably  not  nervous.  (/)  In 
layer  No.  7  are  many  nucleus-like  bodies  \ 

connected  by  radial  fibres  with  the  nervous  cJ[lG-ffQ'~\ 
elements  of  the  rod-and-cone  layer.  Accord-  ™ned  ^tinjj 
ing  to  their  connection  they  are  called  rod-  £de'B8h0°fwt^eg 
granules  and  cowe-granules,  respectively. 

Rods  and  Cones  of  the  Retina,  —  The  struc- 
ture of  layer  No.  9  is  particularly  interest- 
ing. It  consists  of  a  multitude  of  elongated  £"hii"ch  are  8tm 


ORGANS   OF   SENSE   AND  MOTION. 


89 


bodies  arranged  side  by  side,  like  rows  of  palisades. 
These  bodies  are  of  two  kinds,  —  one  cylindrical,  extend- 
ing the  entire  thickness  of  the  layer  (^  inch  long), 
and  called  "  rods  " ;  the  other,  flask-shaped,  shorter,  and 
called  "  cones."  The  inner  ends  of  both  bodies  are 
supposed  to  be  continuous  with  the  fibres  of  the  outer 
nuclear  layer.  Each  rod,  or  cone,  is  composed  of  an  inner 
and  an  outer  segment  or  limb.  The  inner  limb  appears 
under  the  microscope  protoplasmic,  and  feebly  refractile. 
The  outer  limb  is  highly  refractile.  It  has  been  thought 
that  an  extremely  minute  nerve-filament  is  drawn  through 
the  axis  of  these  bodies.  It  is  assumed  that  they  are  con- 
nected with  the  fibrils  of  the  optic  nerve  by  means  of  the 
retinal  nerve-cells  and  radial  fibres. 

In  close  connection  with  the  rods  and  cones  stand  the 
flat  six-sided  cells  of  the  pigment-epithelium.  In  the  cen- 
tre of  the  eye  only  cones  appear,  which  are  here  of  more 
slender  form  and  increased  length ;  so  that  not  less  than 
1,000,000  are  set  in  -j^  inch  square.  Not  far  from  the 
centre  each  cone  is  surrounded  by  a  crown-shaped  border 
of  rods.  Toward  the  ora 
serrata  the  cones  become 
rarer. 

The  Yellow-spot  and  the 
Blind-spot.  —  The  place  of 
clearest  vision,  and  the 
physiological  centre  of  the 
eye,  is  the  "yellow-spot" 
(macula  luted)  ;  it  is  of 
oval  shape,  about  -^  inch 
long,  with  a  depression  in 
the  centre  (fovea  centralis). 

Ahrmf    !    rrF  on   in^n  inforirkv  FIG.  48.  — Equatorial  Section  of  the  Right 

J\  oout  -Q  oi  an  men  interior    Eye  8howing  t£e  Papi]la  of  the  Optic  Ner*  e> 

frrYm      fV>o     mi^rM/a      r»f     fliia       the  Blood-vessels  radiating  from  it,  and  the 

om    tne   middle    ol    tnis    Macu]a  Lutea.  2/i.  (Henie)  s,  sclerotic ;cb, 


spot  is  the  place  where  the    cboroid;  and  R' re 


(Henle.) 
tina. 


90  PHYSIOLOGICAL  PSYCHOLOGY. 

optic  nerve  breaks  into  the  retina.  This  place  is  called 
the  "  blind-spot,"  because  it  can  be  shown  to  be  inoper- 
ative in  vision.  Its  size  varies  considerably  for  different 
eves  (tV  to  yV  inch  long).  It  is  wanting  in  all  the  ner- 
vous elements. 

Photo-chemical  Processes  in  Vision. —  The  physiological  or 
nervous  process  concerned  in  vision  can  be  shown  to 
begin  in  the  rods  and  cones  at  the  back  part  of  the  retina. 
Indeed,  by  throwing  a  strong  light  through  the  cornea, 
and  causing  it  to  be  reflected  within  the  eyeball  before  it 
reaches  the  nervous  elements  of  the  retina  (an  experiment 
devised  by  Purkinje),  it  is  possible  to  perceive  the  arbores- 
cent figure  formed  by  the  shadow  of  the  blood-vessels 
expanded  on  the  front  part  of  our  own  retina.  Yet  the 
rods  and  cones  are  not  directly  irritable  by  light,  so  as  to 
produce  visual  sensation,  —  at  least,  not  unless  the  inten- 
sity of  the  stimulus  be  so  great  as  to  be  injurious  to  the 
nervous  substance  itself.  How,  then,  can  we  see  the 
feeblest  rays  of  the  moon  as  reflected  from  white  paper? 
A  photo-chemical  process  has  accordingly  been  assumed 
to  result  from  the  direct  action  of  the  light ;  and  this 
process  it  is  which  acts  as  the  immediate  stimulus  of  the 
nervous  elements. 

Yet  after  many  careful  experiments,  especially  by  Kiihne 
and  his  pupils,  it  is  difficult  to  establish  the  nature  of  the 
photo-chemical  process  concerned  in  vision,  or  of  the  par- 
ticular pigments  upon  effecting  changes  in  which  the  pro- 
cess is  dependent.  Any  theory  involves,  chiefly,  these  two 
things :  first,  the  decomposition  by  the  light  of  some  sub- 
stance found  in  the  epithelial  elements  of  the  retina ;  and, 
second,  the  action  of  the  decomposition-products  thus 
gained  upon  the  protoplasm  of  the  nervous  end-organs. 
There  seem  to  be  decisive  objections  against  making  the 
pigmentum  nigrum,  or  the  "visual  purple,"  or  any  other 
known  pigment,  the  only  substance  whose  decomposition 


ORGANS   OF   SENSE   AND  MOTION.  91 

by  the  light  is  necessary  to  vision.  And  as  to  the  nature 
of  the  changes  produced  in  the  rods  and  cones  by  the 
decomposition-products  of  any  pigment,  we  are  really  igno- 
rant. A  photo-chemical  theory  of  vision  seems,  therefore, 
to  be  a  desideratum  rather  than  a  scientifically  established 
and  definite  fact. 

The  most  patent  thing  revealed  by  the  structure  of  the 
eye  is  its  adaptation  to  serve  as  the  organ  of  a  highly  differ- 
entiated system  of  intellectual  and  "  geometrical "  sensory 
impressions.  The  fuller  significance  of  this  truth  cannot  be 
understood  until  we  have  made  a  detailed  study  of  those 
series  of  sensations  —  infinitely  varied,  delicately  shaded, 
quickly  successive,  and  speedily  and  firmly  fusing  together, 
as  it  were  —  which  result  from  the  activity  of  this  organ 
of  sense. 

STRUCTURE  OF  THE  EAR. 

The  End-organ  of  Hearing,  like  that  of  vision,  so  far  as 
the  principal  part  of  its  bulk  is  concerned,  consists  of 
mechanical  contrivances  for  applying  the  stimulus  to  the 
genuine  nervous  elements  of  the  special  sense.  The  true 
end-organ  is  the  mechanism  of  epithelial  and  nervous  cells 
which  is  connected  with  the  terminal  fibrils  of  the  special 
nerve  of  this  sense.  A  brief  description  of  the  non-nervous 
structure  is,  however,  desirable  for  our  purpose. 

The  entire  Ear  consists  of  three  parts,  or  ears ;  these 
are  the  external  ear,  the  middle  ear,  or  tympanum,  and 
the  inner  ear,  or  "  labyrinth,"  as  its  complicated  structure 
causes  it  to  be  named. 

I.  The  External  Ear.  —  Exclusive  of  the  .plate  of  carti- 
lage which  projects  from  the  side  of  the  head,  the  external 
ear  consists  of  two  parts.  These  are  the  concha  and  the 
external  meatus.  (1)  The  concha  is  a  rather  deep  hollow 
of  a  shell-like  shape.  It  is  probably  of  little  or  no  use  in 
sharpening  our  acoustic  perceptions ;  although  it  appears 


92  PHYSIOLOGICAL  PSYCHOLOGY. 

to  be  of  some  service  in  discerning  the  direction  of  sound. 
(2)  The  external  meatus  is  a  curved  passage  leading  from 
the  bottom  of  the  hollow  of  the  concha  to  the  drum  of  the 
ear.  Its  most  obvious  office  is  the  protection  of  the  ear- 
drum ;  though  it  may  also  modify  certain  tones  by  its  own 
resonant  action,  —  strengthening  the  high  ones  and  dead- 
ening the  low,  in  some  degree. 

If  we  place  a  resounding  body  in  contact  with  the  teeth, 
the  intensity  of  the  sensation  of  sound  is  much  increased. 
This  appears  to  us  to  be  due  to  direct  conduction  through 
the  cranial  bones;  but  it  is  more  probable  that  the 
principal  path  of  conduction  is  indirect,  through  the  ear- 
drum and  small  bones  of  the  middle  ear  to  the  fenestra 
ovalis. 

II,  The  Middle  Ear,  or  Tympanum.  —  This  part  of  the  or- 
gan of  hearing  is  an  irregular  cuboidal  chamber,  situated 
in  the  temporal  bone,  between  the  bottom  of  the  meatus 
and  the  inner  ear.  Its  outer  wall  is  the  membrana  tympani 

or  "  drum  "  of  the  ear.     In  the 
inner  wall,  which  separates  it 
from  the  labyrinth,  are   two 
,i  openings    called   "windows" 

—  the  fenestra  ovalis  and  the 
fenestra    rotunda.      Near  its 
anterior   part    it    opens  into 
the    Eustachian    tube.      And 
an  irregular  chain  of   bones 

—  called     auditory     bones  — 
.    stretches    across    the    cavity 

FIG.  49.  —  Drum  of  the  Right  Ear  with  J 

the  Hammer,  seen  from  the  .inside.    »/!•    f rom    its     OUter     to     its     inner 
(Henle.)      1,  chorda   tympani;    2,  Eusta- 
chian tube;  *,  tendon  of  the  tensor  tym- 
pani muscle  cut  off  close  to  its  insertion ; 


The   Membrana   Tympani,  or 

Spina  tympanica  posterior.  j)riim  Qf  ^  Ear  __  fbis  mem- 

brane consists  of  three  layers,  —  an  external,  and  internal 
mucous,   and  the   intermediate  membrana  propria.     The 


ORGANS   OF   SENSE  AND   MOTION.  93 

last  is  the  true  vibrating  membrane,  and  is  composed  of 
unyielding  fibres  arranged  both  radially  and  circularly. 

A  flat  membrane,  evenly  stretched,  whose  mass  is  small 
in  proportion  to  the  size  of  its  surface,  is  easily  thrown 
into  vibration  by  acoustic  waves  striking  against  one  of  its 
surfaces.  It  responds  readily  to  tones  which  approach  its 
own  fundamental  tone,  but  is  scarcely  at  all  affected  by 
divergent  tones.  Such  a  membrane,  therefore,  cannot 
repeat  a  motion  which  consists  of  a  series  of  harmonious 
partial  tones.  In  order  to  perform  such  a  service,  a  mem- 
brane must  be  so  arranged  and  connected  as  to  have  no 
preponderating  tone  of  its  own.  For  this  the  ear-drum  is 
prepared  by  two  devices :  (1)  It  is  drawn  inward  into  a 
funnel-shaped  form  by  being  attached  to  one  of  the  auditory 
bones  (the  handle  of  the  malleus) ;  and  (2)  it  is  loaded 
with  a  chain  of  bones  so  as  to  have  no  trace  of  a  tone  of  its 
own  (see  Fig.  50).  Thus  is  secured  for  it  the  property  of 
taking  up  the  vibrations  of  a  large  scale  of  tones. 

Moreover,  since  the  apex  of  its  funnel  bulges  inward, 
the  ear-drum  serves  to  concentrate  the  force  of  the  vibra- 
tions from  all  sides.  Loading  it  with  the  auditory  bones 
serves  also  to  dampen  its  vibrations  and  prevent  them  from 
continuing  too  long.  This  gives  speed  to  the  rate  at  which 
definite  auditory  sensations  can  be  repeated. 

The  Eustachian  Tube,  —  This  opening  from  the  middle 
ear  into  the  mouth  is  of  indirect  but  important  physiolog- 
ical service  to  auditory  sensations.  In  its  normal  position 
the  tube  is  neither  closely  shut  nor  wide  open.  When  we 
swallow,  it  opens  and  thus  effects  a  renewal  of  air  in  the 
middle  ear,  maintains  an  equilibrium  of  pressure  on  both 
sides  the  drum,  and  conveys  away  the  fluids  that  collect 
in  its  cavity.  But  if  it  remained  constantly  wide  open,  we 
should  be  likely  to  hear  our  own  voices  as  a  roaring  sound, 
and.  the  passage  of  the  air  in  and  out  during  respiration 
would  effect  the  tension  of  the  drum. 


94  PHYSIOLOGICAL  PSYCHOLOGY. 

The  Auditory  Bones.  —  The  chain  of  bones  which  stretches 
across  the  tympanic  cavity  consists  of  three  members,  —  the 
Malleus  ("hammer"),  the  Incus  ("anvil"),  and  the  Stapes 
("stirrup ").  The  malleus  has  a  head  separated  by  a  con- 
stricted neck  from  an  elongated  handle.  The  latter  is 
attached  to  the  centre  of  the  membrana  tympani.  The 
incus  has  a  body  and  two  processes.  On  the  front  surface 
of  its  body  is  a  saddle-shaped  hollow.  Its  short  process  is 
bound  by  a  ligament  to  the  posterior  wall  of  the  tym- 
panum. Its  long  process  ends  in  a  rounded  projection  (os 
orbicular  e).  The  /stapes  has  a  head  and  neck,  a  base  and 
two  crura.  These  are  put  together  so  as  to  give  it  the 
stirrup-shape,  which  its  name  implies.  The  manner  in 

which  these  bones  articulate 
may  be  fairly  well  seen  by 
the  accompanying  figure 
(No.  50). 

The  auditory  bones  are 
moved  on  each  other  at  their 
joints  by  two  or  three  mus- 
cles, —  especially  by  the  ten- 
wr  tympani.  This  muscle  is 
inserted  into  the  malleus, 
near  the  root,  and  serves  to 
FIG.  so. -Bols  of  the  Ear,  as  seen  in  tighten  the  tympanic  mem- 

their  connection  from  in  front.  */,.  (Henle.)  Tyro  n  a  Vnr  rlva  \nri-no-  fVi 

I,  Incus  (anvil),  of  which  Ib  is'  the  short;  Drane   DJ  ai  a  Wing  ttl 

and  II  the  long,  process ;  c,  its  body,  and  \ n ,xrp rrj         TliA    anrmafir* 

pi.  the  process  for  articulation  with   the  UOTraiO- 

tions,  imparted  by  the  mem- 
brane to  these  bones,  are  not 
with  us  capituium,cP.  •   longitudinal    but   transverse. 

They  do  not,  however,  resemble  the  vibrations  of  a  stretched 
cord  or  a  fixed  pin.  The  bones  vibrate  as  a  system  of  light, 
small  levers,  with  a  simultaneous  motion  around  a  common 
axis.  The  vibrations  are  sympathetic,  and  vary  greatly 
for  tones  of  different  pitch  and  similar  intensity. 


ORGANS    OF    SENSE   AND    MOTION. 


95 


General  Office  of  the  Middle  Ear.  —  By  this  part  of  the 
organ  of  hearing  the  acoustic  waves  are  transmitted  to  the 
inner  ear,  while  their  character  is  greatly  modified.  Mod- 
ification is  necessary  to  prepare  the  stimulus  for  the  organ- 
ism of  the  inner  ear.  The  waves  in  the  air,  when  they 
reach  the  ear-drum,  have  a  large  amplitude  but  a  compara- 
tively small  intensity.  Their  motion  must  be  changed 
into  one  of  diminished  amplitude  and  increased  intensity. 
But  the  transmitting,  vibrating  media  must  also  have  the 
power  of  answering  to  the  different  tones  of  any  pitch 
perceptible  by  the  ear. 

III.  The  Internal  Ear,  or  Labyrinth.  —  It  is  in  this  mar- 
vellously complex  organ  that  the  terminal  fibrils  of  the 
auditory  nerves  are  distributed  and  the  end-organs  of  hear- 
ing are  placed.  It  consists  of  three  parts  —  the  Vestibule, 
the  Semicircular  Canals,  and  the  Cochlea.  Each  of  these 
parts  is,  as  it  were,  made  twice  over  —  once  in  the  form  of 
channels  cut  in  the  petrous  bone  (the  osseous  vestibule, 
etc.),  and  again  in  the  form  of  a  membrane  (the  membra- 
nous vestibule,  etc.)  suspended  in  the  bony  cavity,  but  only 
partly  filling  it. 


No.  1. 


No.  2. 


No.  3. 


Tsf 


FIG.  51.  — No.  1,  Osseous  Labyrinth  of  the  Left  Ear,  from  below;  No.  2,  of  the 
Right  Ear,  from  the  inside;  No.  3,  of  the  Left  Ear,  from  above.  (Henle.)  Av,  aque- 
duct of  vestibule  ;  Fc,  fossa  of  the  cochlea  ;  Fee,  its  fenestra  (rotunda)  ;  Fv,  fenestra 
of  the  vestibule  (ovalis);  ha,  external  ampulla;  h,  external  semicircular  canal;  Tsf, 
tractus  spiralis  foraminosus  ;  vaa,  ampulla  of  the  superior  semicircular  canal;  vc,  pos- 
terior semicircular  canal  ;  and  vpa,  its  ampulla. 

(J.)  The  Vestibule  of  the  Ear.  —  The  central  cavity  of 
the  inner  ear,  called  the  "vestibule,"  is  the  earliest 


96 


PHYSIOLOGICAL   PSYCHOLOGY. 


Ls 


and  most  constant  part  of  the  labyrinth.  In  its  outer  wall 
is  the  fenestra  ovalis ;  its  anterior  wall  communicates  with 
the  scala  vestibuli  of  the  cochlea.  The  membranous  vesti- 
bule is  composed  of  two  sac-like  dilatations  —  the  upper 
and  larger  called  utriculus,  the  lower  sacculus. 

(j?)  The  Semicircular  Canals,  —  These  curved  channels 
open  into  the  utriculus.  They  are  three  in  number, 
about  one  inch  in  length  and  ^V  inch  in  diameter.  They 
have  a  regular  relative  position  —  their  planes  being  at 
right  angles  to  each  other  —  as  indicated  by  their  names 
—  superior,  posterior  or  vertical,  and  external  or  horizon- 
tal (see  Fig.  51).  Near  the  vestibule  they  dilate  into  the 
so-called  ampullae. 

Both  the  osseous  vestibule  and  the  osseous  canals  contain 
a  fluid  {perilympti)  in  which  the  corresponding  membra- 
nous parts  —  themselves 
distended  with  a  fluid  (en- 
dolymph)  —  are  suspended. 
The  office  of  this  fluid  is 
very  important  in  the  trans- 
mission and  further  modi- 
fication of  the  acoustic 
waves. 

(<?)  The  Cochlea.  — This 
wonderful  organ  is  shaped 
like  the  shell  of  a  common 
snail,  about  \  inch  long. 
It,  too,  consists  of  a  mem- 
branous sac  in  an  osseous 
cavity.  The  whole  passage 
is  imperfectly  divided  into 
two  canals  by  a  partition- 
wall  of  bone  (the  lamina 
spiralis),  which  winds  2J 
times  around  an  axis  (the  modiolus),  like  a  spiral  staircase. 


Fee 

FIG.  52.  — Osseous  Cochlea  of  the  Right 
Ear,  exposed  from  in  front.  4/i-  (Henle.) 
t,  section  of  the  division-wall  of  the  cochlea; 
tt,  upper  end  of  the  same;  Fee,  fenestra; 
H,  hamulus;  Md.modiolus;  Ls,  lamina  spira- 
lie. 


ORGANS    OF    SENSE   AND   MOTION. 


97 


Liyatnentui* 
spirale 


Lamina 

basilaris 


FIG.   53.  — Section   through   one  of   the  Coils  of    the 
Cochlea.    20/1-     (Schematic,  from  Gegenbaur.) 


Of  these  canals,  the  one  which  faces  the  base  is  called  scala 
tympani;  the  other,  which  opens  into  the  vestibule  is  the 
scala  vestibuli.    At 
the  apex  they  com- 
municate   through 
a   small  hole  (the 
helicotrema).  From 
the    free    edge    of    \  $ 

the  spiral  lamina 
to  the  outer  wall 
the  interval  is 
bridged  over  by 
the  basilar  mem- 
brane. Still  an  other 
membrane  (mem- 
brane of  Reissner) 
arises  from  a  crest  attached  to  the  same  lamina  and  ex- 
tends to  the  outer  wall,  so  as  to  make  a  minute  canal 
between  itself  and  the  basilar  membrane.  In  this  canal 
—  called  scala  intermedia,  or  ductus  cochlearis,  or  "  canal 
of  the  cochlea  "  —  the  nervous  end-organs  of  the  cochlea 
are  found. 

The  Organ  of  Corti.  —  On  that  surface  of  the  basilar  mem- 
brane which  is  directed  toward  the  small  canal  of  the 
cochlea  is  placed  a  structure  which  consists  of  a  wonder- 
ful arrangement  of  cells.  Some  of  these  cells  are  curved, 
elongated,  and  placed  in  two  groups  —  an  inner  and  an 
outer  (rods,  or  fibres  of  Corti).  The  two  are  arranged  (as 
shown  by  Fig.  54)  so  as  to  make  a  bow  or  arch  over  an 
exceedingly  minute  canal  (canal  of  Corti)  between  them 
and  the  basilar  membrane.  These  rods  of  Corti  increase 
in  length  from  the  base  to  the  apex  of  the  cochlea.  Each 
rod  rests  upon  one  or  two  of  the  transverse  fibres  of  the 
basilar  membrane.  The  Organ  of  Corti  is  separated  from 
the  endolymph  of  the  ductus  cochlearis  by  the  so-called 


98 


PHYSIOLOGICAL  PSYCHOLOGY. 


membrana  tectoria.  (For  the  shape  and  position  of  the 
"hair-cells,"  inner  and  outer,  the  supporting  cells,  etc., 
see  the  accompanying  diagrammatic  representation.) 


n  ' 


FIG.  54.  — Organ  of  Corti  in  the  Dpg.  8°%.  (Waldeyer.)  b— c,  homogeneous  layer 
of  the  basilar  membrane;  «,  its  yestibular  layer;  v,  its  tympanal  layer;  d,  blood-vessel; 
f,  nerves  in  spiral  lamina;  g,  epithelium  of  spiral  groove;  h,  nerve-fibres  passing  toward 
inner  hair-cells  i,  k;  I,  auditory  hairlets  on  inner  hair-cells;  I— Zj  lamina  reticularis;  TO, 
heads  of  the  rods  of  Corti  jointed  together;  the  inner  rod  seen  in  its  whole  length;  the 
outer  one  broken  off;  n,  cell  at  base  of  inner  rod;  p,  q,  r,  outer  hair-cells;  s,  a  cuticular 
process  probably  belonging  to  a  cell  of  Deiters;  t,  lower  ends  of  hair-cells,  two  being 
attached  by  cuticular  processes  to  the  basilar  membrane;  w,  a  nerve-fibril  passing  into  an 
outer  hair-cell;  z,  a  sustentacular  cell  of  Deiters. 

Distribution  of  the  Auditory  Nerve,  —  The  auditory  nerve, 
on  approaching  the  labyrinth,  divides  into  several  portions. 
In  the  vestibule,  branches  are  distributed  to  the  utriculus, 
the  sacculus,  and  each  of  the  three  ampullae.  In  a  ridge  in 
the  wall  of  each  of  these  dilatations  (the  crista  acoustica) 
columnar  and  fusiform  cells  are  found,  with  processes  from 
the  latter  of  which  the  fibrils  of  the  auditory  nerve  are 
brought  into  connection,  —  probably  by  means  of  that 
minute  network  of  fibrils  with  which  we  have  already 
become  familiar  in  the  other  end-organs  of  sense.  The 
so-called  "  auditory  hairs  "  are  found  by  recent  observers 
to  be  connected  with  the  columnar  cells  ;  they  form,  on  the 
inner  surface  of  the  epithelium  of  the  ridge  a  "  thick-set 


ORGANS   OF   SENSE   AND  MOTION. 


99 


wood."  Calcareous  particles  exist  (the  otoliths  or  "ear- 
stones  ")  in  both  saccule  and  utricle,  lying  embedded  in 
contact  with  the  nerve-epithelium. 

The  cochlean 
branch  of  the  audi- 
tory nerve  pierces 
the  modiolus  and 
gives  off  lateral 
branches  which  pass 
into  channels  in  the 
osseous  spiral  lamina. 
Here  the  fibres  radi- 
ate to  the  membra- 
nous lamina  and  are 
connected  with  a 
ganglion  of  cells. 
Beyond  this  gangli- 
on they  lose  their  me- 
dullary sheath,  and 
become  extremely 
fine  axis-cylinders, 
the  delicate  fibrils 

FIG.  55.  —  Scheme  of  the  Nerve-endings  in  the  Am- 

of    which   are    Droba-      pullae.    (After  Rudinger.)     1,  membranous  wall  of  the 
ampullae,  with  a  structureless  border  2,  through  which 

blv   Connected      With      *ne  nerve-fibre  3,  sends  its  axis-cylinder  4;  5,  plexiform 
*  connection  of  the  nerve-fibres ;  6,  auditory  cells;  7,  sup- 

the    nerve-pleXUS     Of      porting  cells ;  8,  auditory  hairs. 

the  fibrils  from  the  cone-cells  of  the  organ. 

Special  Office  of  the  Labyrinth.  —  The  greater  bulk  of  the 
inner  ear,  like  the  whole  of  the  other  principal  parts,  is 
used  to  transmit  and  modify  the  acoustic  waves.  We  have 
seen  that  the  membranous  labyrinth  is  filled  with,  and  sus- 
pended in,  a  fluid  medium.  Molecular  oscillations  of  this 
fluid  can  scarcely,  however,  serve  as  the  direct  stimulus  of 
the  nerve-elements.  Its  dimensions  are  so  very  small  in 
comparison  with  the  length  of  the  acoustic  waves  as  trans- 
mitted by  the  shocks  of  the  stirrup  at  the  fenestra  ovalis. 


100  PHYSIOLOGICAL   PSYCHOLOGY. 

or  the  pulsations  of  air  at  the  fenestra  rotunda,  that  the 
movement  of  the  entire  fluid  mass  would  be  practically 
instantaneous.  Several  places  may  be  pointed  out,  how- 
ever, into  which  the  waves  of  the  fluid  could  retreat,  by 
the  membranes  yielding,  or  by  itself  running  into  pores  and 
through  the  passages  connecting  the  various  parts.  The 
friction  of  these  movements  back  and  forth,  especially  when 
increased  by  the  action  of  the  otoliths,  might  thus  irritate 
the  nerve-elements.  The  basilar  membrane  would  undoubt- 
edly be  thrown  into  vibration  by  the  unequal  pressure  of 
the  fluid,  and  thus  the  nervous  structures  situated  upon  it 
might  be  irritated.  In  all  this,  however,  much  is  still  a 
matter  of  doubtful  conjecture. 

A  still  more  difficult  question  to  answer  is  this :  How 
does  the  ear  manage  to  analyze  the  acoustic  influences? 
This  organ  plainly  is  not  contrived  so  as  to  reproduce 
changes  in  the  form  of  acoustic  oscillations  in  such  manner 
that  these  changes  can  be  made  apparent  to  the  eye  or  to 
touch.  But  our  experience  with  "  clangs,"  or  the  musical 
notes  of  ordinary  kind,  seems  to  require  that  we  should 
find  in  the  ear  some  sympathetic  vibratory  apparatus. 
Such  apparatus  must  suffice  for  all  kinds  of  noises,  and  for 
all  musical  tones,  and  for  simultaneous  hearing  of  several 
tunes  as  harmony,  and  for  so  rapid  a  succession  of  different 
sensations  as  occurs  when  we  hear  a  melody,  or  even  the 
crackling  of  an  electric  spark  at  intervals  of  0.002  sec. 

It  has  been  for  some  time  commonly  assumed  that  the 
vestibule  and  semicircular  canals  are  the  organs  for  hear- 
ing noises,  and  the  cochlea  for  hearing  musical  sounds. 
This  differentiation  of  function  is  certainly  suggested  by 
the  marked  differences  in  the  structure  of  their  parts. 
The  otoliths  and  hairs  of  the  former  do  not  seem  adapted 
for  regular  sympathetic  vibrations.  The  rods  of  Corti  and 
radii  of  the  basilar  membrane  suggest  that  here  is  the 
apparatus  needed  for  acoustic  analysis. 


7 
ORGANS   OF   SENSE  AND   MOTION.  101 

Recent  investigations,  however,  tend  to  show  that  the 
physiological  distinction  between  noises  and  sounds  will 
not  hold  with  sufficient  rigor.  The  two  seem  to  pass  into 
each  other  by  insensible  gradations.  It  has  been  found 
possible  to  make  a  series  of  sharp  noises,  like  a  watchman's 
rattle,  as  often  as  600  times  per  second,  without  producing 
a  musical  tone,  if  all  extra  accompanying  sounds  are  com- 
pletely dampened.  On  such  grounds  it  has  been  concluded 
that  we  hear  noises  and  tones  with  the  same  organ. 

It  was  first  argued  by  Helmholtz  that  the  fibres  of  Corti 
—  some  3000  in  number  and  arranged  in  rows  on  the 
basilar  membrane  like  the  keys  of  a  piano-forte  —  are 
just  suitable  for  the  required  sympathetic  vibrations. 
But  these  rods  are  stiff  and  not  easily  vibratory,  and  their 
office  seems  to  be  that  of  supporting  the  hair-cells.  Birds, 
moreover,  can  appreciate  musical  notes  but  have  no  rods  of 
Corti.  It  has  therefore  been  proposed  by  Hensen  and  others 
to  regard  the  radii  of  the  basilar  membrane  as  themselves 
graded  to  pitch.  These  radii,  by  moving  up  and  down, 
might  excite  the  conical  hair-cells,  whose  number  is  sup- 
posed to  be  about  sufficient  to  satisfy  the  demands  of 
musical  analysis.  More  recently  still,  it  has  been  conjec- 
tured that,  since  the  arches  of  Corti  at  the  base  of  the 
cochlea  are  small  and  little  spread,  and  those  at  the  uppor 
end  are  larger  and  much  spread,  the  size  and  the  shape  of 
these  structures  may  approximately  compensate  each  other ; 
this  would  make  it  possible  for  all  of  the  arches  to  vibrate 
to  each  of  the  fibres  of  the  basilar  membrane  (like  the 
sounding-board  of  a  piano). 

We  are  obliged  to  confess  that  our  knowledge  of  the 
minutest  structure  of  the  ear,  and  especially  of  the  manner 
in  which  it  performs  its  functions,  is  exceedingly  frag- 
mentary. As  one  principal  investigator  remarks:  "It 
is  possible  that  the  working  of  this  apparatus  may  be 
altogether  different  from  any  of  our  present  conjectures." 


102  PHYSIOLOGICAL  PSYCHOLOGY. 

END-ORGANS  OF  MOTION. 

The  motor  nerves  of  animals  have  their  peripheral  con- 
nection with  either  electrical  organs,  or  secretory  glands, 
or  muscular  fibre.  A  very  brief  consideration  of  the  last 
case,  only,  will  suffice  for  our  present  purpose. 

After  a  motor  nerve  has  entered  the  substance  of  the 
so-called  voluntary  or  striated  muscle  it  breaks  up  into 
nerve-twigs  between  the  muscular  fibres.  The  axis-cyl- 
inders of  the  nerve-twigs  lose  their  medullary  sheath,  and 
subdivide  into  fibrils,  which  form  a  flat  branching  mass 
within  certain  disk-shaped  bodies  inside  the  sheath  of  the 
muscle-fibre  (the  sarcolemma).  These  bodies  are  the  so-called 
"  motor  end-plates."  In  the  non-striated  (or  non-voluntary) 
muscles,  the  nerves  subdivide  into  very  minute  plexuses 
of  nerve-fibres,  which  are  distributed  in  the  connective 
tissue  that  separates  the  muscular  fibres. 

The  shape  and  structure  of  the  motor  end-plates  are 
different  for  different  animals,  and  even  for  different  mus- 
cles of  the  same  animal.  The  mode  of  the  termination  of 
the  nerve  in  the  muscle  is  thought  to  be  somewhat  dis- 
tinctive of  the  different  parts  of  the  muscular  structure. 
Sometimes  the  axis-cylinders  are  enlarged,  with  granular 
corpuscles  attached  or  adjacent.  Sometimes  a  granular 
mass,  with  its  nuclei,  forms  a  kind  of  floor  for  the  terminal 
nerve-fibres ;  and  this  eminence  may  be  either  elongated, 
elliptical,  or  circular. 


CHAPTER  IV. 

DEVELOPMENT  OF  THE  NERVOUS  SYSTEM. 

IN  that  living  germ,  in  which  the  life  of  the  individual 
human  being  originates,  there  is  no  apparent  distinction  of 
bodily  organs,  or  of  physical  and  psychical  activities.  To 
scientific  observation  this  germ  seems  "  undifferentiated." 
But  it  undergoes  a  development,  and  before  it  can  be  sub- 
jected to  ordinary  observation  it  has  unfolded  itself  into 
an  elaborate  organism.  The  course  of  this  development 
can  be  traced,  in  man's  case,  only  very  imperfectly  by  even 
the  most  patient  embryological  investigation. 

Fortunately,  however,  the  very  first  things  in  the  life  of 
the  other  mammals,  and  even  of  the  chick  (the  most  con- 
venient subject  of  study  for  embryology)  are  in  most 
important  respects  similar  to  those  of  man's  earliest  devel- 
opment. This  knowledge,  indirectly  derived,  is  constantly 
being  more  and  more  supplemented  by  direct  microscopic 
inspection  of  the  human  embryo,  at  various  stages  in  its 
life.  Thus  a  sketch  of  the  principal  outlines  of  man's 
pre-natal  evolution  is  made  possible.  A  few  points  selected 
from  such  a  sketch,  and  having  reference  especially  to  the 
nervous  system,  furnish  helpful  suggestions  with  regard  to 
certain  questions  in  physiological  psychology. 

EARLIEST  DEVELOPMENT  OF  THE  BODILY  LIFE. 

The  following  brief  description  of  the  earliest  develop- 
ment of  the  animal  body  is  chiefly  taken  from  the  detailed 
embryology  of  the  common  fowl.1 

1  For  further  study  of  this  subject,  Foster  and  Balfour's  Elements  of 
Embryology,  London,  will  probably  be  found  most  accessible  and  ser- 
viceable. 

103 


104  PHYSIOLOGICAL  PSYCHOLOGY. 

The  Ovarian  Ovum.  —  The  immature  egg  (ovarian  ovum) 
of  any  animal  presents  the  characters  of  a  simple  cell.  It 
appears  as  a  naked  protoplasmic  body  containing  in  its 
interior  a  nucleus  (germinal  vesicle),  and  within  this  a 
nucleolus  (the  germinal  spot).  It  is  enclosed  in  a  capsule 
of  epithelium  called  the  "  follicular  membrane."  The 
principal  difference  between  the  ovum  of  a  mammal  and 
that  of  a  bird  consists  in  the  amount  and  distribution  of 
the  food-yolk.  The  human  ovarian  ovum  is  only  y^  to 
yj-g-  inch  in  diameter,  because  it  contains  so  little  food- 
yolk  ;  but  this  small  supply  is  uniformly  distributed. 

As  the  ovum  matures,  its  body  grows  in  size,  and  gran- 
ules appear  in  the  interior.  As  these  earliest  granules 
enlarge,  others  appear  at  the  periphery.  The  germinal 
vesicle  travels  toward  the  surface,  and  accessory  germinal 
spots  make  their  appearance.  The  cells  of  the  follicular 
membrane  —  at  first  a  single  row  —  now  become  two  or 
three  deep.  The  superficial  layer  of  the  ovum  is  converted 
into  a  striated  membrane.  Between  this  and  the  cells  of 
the  follicular  membrane  another  membrane  (the  vitelline) 
afterward  appears.  The  striated  membrane  disappearing, 
the  vitelline  remains  alone.  But  the  essential  constituent 
of  the  body  of  the  ovum  is  an  active,  living  protoplasm. 

Impregnation  and  Segmentation.  —  The  spermatozoon,  or 
male  fecundating  element,  may  itself  be  considered  as  a 
cell,  the  nucleus  of  which  is  its  head.  Impregnation 
takes  place  by  the  entrance  of  a  spermatozoon  into  the 
ovum,  followed  by  the  fusion  of  the  two.  On  entering, 
the  substance  of  the  tail  of  the  spermatozoon  mingles  with 
the  protoplasm  of  the  ovum,  while  the  head  enlarges  and 
also  fuses  with  a  portion  of  the  ovum,  thus  constituting 
the  nucleus  of  the  impregnated  egg.  In  this  actual  fusion 
of  substance  derived  from  both  parents,  provision  is  made 
that  the  offspring  shall  partake  of  the  physical  and  psy- 
chical characteristics  of  the  two. 


DEVELOPMENT    OF   THE   NERVOUS    SYSTEM.  105 

Segmentation,  or  "  yolk-cleavage,"  follows  fecundation  of 
the  ovum.  This  process  consists  in  dividing  the  ovum 
into  a  number  of  cells  from  which  all  the  cells  of  the  full- 
grown  animal  are  the  lineal  descendants.  The  germinal 
disk  of  the  ovum  is  thus  broken  up  into  a  large  number  of 
rounded  segments  of  protoplasm,  called  the  blastoderm. 
The  upper  segments  being  smaller  than  those  beneath,  the 
beginning  of  two  layers  is  thus  made.  This  distinction 
is  then  made  more  obvious  by  the  segments  of  the  upper 
layer  arranging  themselves  side  by  side  into  a  membrane 
of  columnar,  nucleated  cells ;  but  the  segments  of  the 
lower  layer  continue  granular,  and  form  a  close,  irregular 
network  of  cells. 

As  the  process  of  segmentation  goes  on,  the  differences 
among  the  ova  of  different  species  of  animals  become  more 
clearly  marked.  The  mechanical  explanation  of  this  is,  in 
part  at  least,  the  difference  in  the  amount  and  distribution 
of  the  food-yolk. 

The  Blastodermic  Vesicle.  —  A  narrow  cavity  now  appears 
between  the  two  layers  of  the  ovum,  which  soon  extends 
so  as  to  separate  them  completely,  except  in  the  region 
near  a  small  circular  area.  In  this  area  the  inner  mass  of  the 
ovum  has  remained  longer  than  elsewhere  exposed,  before 
the  outer  cells  closed  over  it.  The  enlargement  of  the 
ovum,  and  of  the  cavity  between  the  layers,  gives  the 
whole  structure  the  appearance  of  a  vesicle  with  a  thin 
wall.  It  is  therefore  now  called  the  blastodermic  vesicle. 
Its  walls  are  for  the  most  part  composed  of  a  single  row  of 
outer  flattened  cells ;  while  an  inner  lens-shaped  mass  of 
cells  appears  attached  to  a  portion  of  the  inner  side  of  the 
outer  layer.  As  the  vesicle  grows  rapidly,  this  inner 
mass  becomes,  on  the  whole,  flattened  so  as  to  spread  out 
on  the  inner  side  of  the  outer  layer.  But  its  central  part 
remains  thick,  and  forms  an  opaque  spot,  which  is  the 
beginning  of  the  area  where  the  embryo  is  to  form  (the 
embryonic  area). 


106 


PHYSIOLOGICAL  PSYCHOLOGY. 


FIG.  56.  —  Vascular  Area  and  Embryonic  Area  of  the  Embryo  of  a  Rabbit,  seven  days 
old.  w/!.  (Kb'lliker.)  o,  o,  the  vascular  or  opaque  area;  agt  embryonic  area;  pr, 
primitive  streak  and  groove;  rf,  medullary  groove. 

The  Three  Layers  of  the  Embryo.  —  In  the  area  just 
described  there  are  first  formed  two  distinct  strata.  Of 
these,  the  upper  one  consists  of  rounded  cells,  which  lie 
close  to,  and  become  fused  with,  the  flattened  outer  layer ; 
it  is  then  called  epiblast.  The  lower  one  consists  of 
flattened  cells,  and  is  called  hypollast.  We  have  thus  a 
double-walled  sac  (the  gastrula).  Between  these  two 
strata,  or  layers,  a  third  soon  makes  its  appearance ;  from 
its  position  it  is  called  mesoblast. 

These  three  layers  are  found  in  the  embryo  of  all  ver- 
tebrate, and  of  most  invertebrate,  animals  ;  and  from  them 
all  the  different  parts  of  the  animal  organism  are  developed. 
The  history  of  the  life  of  every  animal,  thus  constituted, 

is  in  its  earlier  stages  a  history  of  the  evolution  of  these 

j 

layers.     The  hypoblast  is  the  secretory  layer ;  and  from  it 
almost  all  the  epithelial  lining  of  the  alimentary  tract,  and 


DEVELOPMENT   OF   THE   HERVOUS   SYSTEM.  107 

of  its  glands,  is  derived.  From  the  mesoblast  come  the 
skeletal,  muscular,  and  vascular  systems,  and  the  connec- 
tive tissue  of  all  parts  of  the  body.  But  it  is  the  develop- 
ment of  the  epiblast  which  most  concerns  us.  For  from 
it  is  evolved  the  central  and  peripheral  nervous  system, 
the  epidermis,  and  the  most  important  parts  of  the  organs 
of  sense. 

From  the  beginning,  then,  the  skin  in  which  the  end-organs 
of  touch  and  of  the  other  sensations  are  situated,  as  well  as 
all  the  organs  of  special  sense,  constitute,  with  the  brain  and 
spinal  cord,  one  interconnected  mechanism. 

DEVELOPMENT  OF  THE  NERVOUS  SYSTEM. 

The  process  of  differentiating  the  layers  of  the  blasto- 
derm is  intimately  connected  with  another,  in  which  the 
foundations,  as  it  were,  of  the  nervous  structure  are  laid. 
This  is  — 

The  Formation  of  the  Medullary  Groove.  —  A  short  sickle- 
like  thickening,  due  to  a  forward  propagation  ("linear 


eift 


FIG.  57.  — Primitive  Streak  of  the  Embryo  of  a  Rabbit,  eight  days  and  nine  hours  old. 
220/1.  (Kolliker.)  No  medullary  groove  has  yet  been  formed,  ax,  primitive  streak;  pr, 
primitive  groove ;  pf,  primitive  fold ;  ect,  ectoderm  (or  epiblast) ;  mes,  mesoderm  (or 
mesoblast) ;  ent,  entoderm  (hypoblast). 

proliferation  ")  of  epiblastic  cells  in  a  straight  line,  occurs 
near  the  junction  between  the  pellucid  and  the  opaque 
areas,  and  stretches  inward  upon  the  embryonic  area.  It 
is  called  the  primitive  streak.  Its  middle  line  then  shows 


108  PHYSIOLOGICAL  PSYCHOLOGY. 

a  shallow  furrow  called  the  primitive  groove  (see  Fig.  57). 
In  the  embryonic  area,  to  the  front  of  the  primitive  streak, 
the  axial  part  of  the  epiblast  thickens ;  two  folds  arise 
along  the  boundaries  of  a  shallow  groove ;  the  folds  meet 
in  front  but  diverge  behind,  enclosing  between  them  the 
front  part  of  the  streak.  These  are  the  medullary  folds,  — 
the  first  definite  features  of  the  embryo. 

The  part  enclosed  between  the  medullary  folds  is  called 
the  "  medullary  plate  " ;  it  is  the  portion  of  the  epiblast 
which  gives  rise  to  the  central  nervous  system. 

The  Notochord  and  the  Neural  Canal.  —  Meanwhile  an 
important  change  has  taken  place  in  the  hypoblast,  in 
front  of  the  primitive  streak.  An  opaque  line  has  ap- 
peared, running  forward  from  the  front  end  of  the  streak, 
and  stopping  short  at  a  semicircular  fold  near  the  front  part 
of  the  pellucid  area.  This  opaque  line  is  a  concentration 
of  cells  in  the  form  of  a  cord,  —  the  so-called  Notochord. 
Changes  in  it  are  to  give  rise  to  the  distinctively  vertebral 
structure  of  the  animal.  The  fold  is  the  future  head-fold. 

And  now  a  portion  of  the  blastoderm  in  the  pellucid 
area,  heretofore  nearly  flat,  is  "  tucked  in,"  with  the  form 
of  a  crescent.  Looked  at  from  above,  this  tuck  appears  as 
a  curved  line  along  the  margin  of  the  medullary  groove. 
Thus  the  blastoderm  becomes  at  this  spot  folded  in  the 
form  of  the  reversed  letter  g  (the  "head-fold"  already 
referred  to).  The  upper  limb  of  the  fold  grows  forward, 
the  lower  backward.  As  the  fold  enlarges,  the  crescentic 
groove  deepens  and  its  overhanging  margin  rises  above  the 
level  of  the  blastoderm. 

Meanwhile  the  medullary  folds  increase  in  height  and 
lean  over  toward  the  middle  line.  They  soon  come  into 
contact  in  the  brain-region,  although  they  do  not  at  once 
coalesce.  They  thus  form  a  tubular  canal,  called  the 
Neural  (or  medullary)  canal.  By  the  closing  of  the  folds 
in  the  head-region,  the  open  medullary  groove  has  now 


DEV 


OF  THE   NERVOUS   SYSTEM. 


109 


•A  bl 


become  converted  into  a  tube,  which  is  closed  in  front  but 
remains  open  behind. 

Formation  of  the  Cerebral  Vesicles.  —  The  front  end  of  the 
neural  canal  has  a  more  rapid  V 

growth  than  the  rest.  It 
swells  into  a  small  bulb  or 
vesicle,  whose  cavity  is  con- 
tinuous with  the  neural  canal, 
while  its  walls  are  formed  of 
the  epiblast.  This  bulb  is  the 
first  "  brain-bud,"  or  cerebral 
vesicle.  From  its  sides  the 
processes  of  the  optic  vesicles 
soon  grow  out.  Behind  the 
first  vesicle  a  second,  and 
behind  the  second  a  third, 
is  soon  formed.  Thus  there 
come  to  be  three  brain-buds, 
or  germinal  brains.  From 
them  are  to  develop  the  fore- 
brain,  the  mid-brain,  and  the 
hind-brain. 

Flexure  of  the  Neural  Canal. 
—  The  fore-brain  vesicle,  or 
front  part  of  the  neural  canal, 
becomes  bent  downward 
through  inequalities  of 

growth.       Bv  increase  Of  this     Mne  veins ;°Mr,  medullary  canal,  spinal 
*  .  .        part;  Mr  '.medullary  wall  of  the  mid-brain; 

flexure    the    front    portion    is      Uw>  proto-vertebral  somites. 

folded  down  so  that  the  second  vesicle,  or  mid-brain,  pro- 
jects in  front  of  it. 

All  the  subsequent  development  of  the  nervous  system 
is  connected  with  the  growth  of  the  three  cerebral  vesicles 
and  the  flexure  of  the  neural  or  medullary  canal. 

Development  of  the  Cerebral  Vesicles.  —  From  the  front 


Mr 


FIG.  58.  — Fore-part  of  an  Embryo-chick 
at  the  end  of  the  second  day,  viewed  from 
the  Dorsal  Side.  1/70-  (Kolliker.)  Vh,  fore- 
brain;  Abl,  ocular  vesicles;  Mh,  mid- 
brain  ;  Hh,  hind-brain ;  H,  part  of  the  heart 
seen  bulging  to  the  right  side;  Vom,  vitel- 


iio 


PHYSIOLOGICAL  PSYCHOLOGY. 


part  of  the  fore-brain  the  vesicles  of  the  cerebral  hemi- 
spheres swell  out.  Each  of  these  lateral  brain-buds  has  a 
cavity  which  is  continuous  with  the  cavity  of  the  fore- 
brain.  The  cavities  on  either  side  become  the  lateral 


Plexus 
chorioides 


Mid-brain 


Hind-brain 
Rudimentary 
cerebellum 
&  medulla 


Foramen 
Monroi 


N.  opt. 


Infundi- 
bulum 


N.  trig. 


FIG.  59.  —  A,  Brain  of  an  Embryo  of  the  Rabbit.  R,  Brain  of  an  Embryo  of  the  Ox. 
In  both  cases  the  side- wall  of  the  left  hemisphere  is  removed.  (After  Mihalkovics.) 

ventricles  of  the  brain.  The  original  vesicle  of  the  fore- 
brain,  having  ceased  to  occupy  its  front  position,  develops 
into  the  parts  around  the  third  ventricle.  The  front 
portion  of  the  third  cerebral  vesicle  is  now  marked  off  by 
a  constriction ;  thus  the  hind-brain  is  separated  into  two 
parts,  —  the  rudimentary  cerebellum  with  the  pons  in 
front,  and  the  rudimentary  medulla  oblongata. 

The  following  table  —  taken  from  the  ninth  edition  of 
Quain's  Anatomy,  exhibits  the  relation  in  which  the  de- 
veloped parts  of  the  brain  stand  to  its  fundamental  rudi- 
ments :  — 


DEVELOPMENT   OF  THE  NERVOUS   SYSTEM. 


Ill 


I. 

Anterior  Pri- 
mary Vesi- 
cle. 

1.  Prosencephalon, 
Fore-brain, 

I 

Thalarnen-cephalon, 
2.  Inter-brain, 

II. 

Middle  Pri- 
mary Vesi- 
cle. 

III. 

Posterior  Pri- 
mary Vesi- 
cle. 


Mesencephalon, 
I  3.  Mid-brain, 

4.  Epencephalon, 
Hind-brain. 


Metencephalon, 
5.  After-brain. 


f  Cerebral  Hemispheres,  Corpora 
Striata,  Corpus  Callosum, 
Fornix,  Lateral  Ventricles, 
Olfactory  Bulb?. 

Thalami  Optici,  Pineal  Gland, 
Pituitary  Body,  Third  Ven- 
tricle, Optic  Nerve  (prima- 
rily). 

f  Corpora  Quadrigemina,  Crura 

<  Cerebri,  Aqueduct  of  Sylvius, 
I    Optic  Nerve  (secondarily). 

f  Cerebellum,  Pons  Varolii,  an- 

<  terior  part   of    the    Fourth 
[    Ventricle. 

f  Medulla    Oblongata,    Fourth 
I    Ventricle,  Auditory  Nerve. 


The  Cranial  and  Spinal  Nerves, — Along  the  cerebrospi- 
nal  cavity  —  formed  as  described  above  —  various  changes 
in  the  lining  of  the  epiblast  take  place.  This  lining  is 
thickened  at  the  side  so  that  the  cavity  comes  to  resemble 
a  narrow  vertical  slit.  The  sides  and  floor  of  the  canal  of 
the  cerebral  hemispheres  are  also  much  thickened.  But 
in  the  region  of  the  third  and  fourth  ventricles  the  roof  of 
the  canal  becomes  very  thin. 

The  cranial  nerves  spring  out  of  a  band,  composed  of  two 
plates,  which  connects  the  dorsal  edges  of  the  neural  canal 
with  the  external  epiblast.  The  fusing  of  the  two  plates 
makes  the  band  into  a  crest  on  the  roof  of  the  brain.  As 
the  roots  of  the  cranial  nerves  grow  centrifugally  and 
become  established,  the  connecting  crest  is  partially  obliter- 
ated. In  its  earliest  stages  a  cross-section  of  the  brain-tube 
is  essentially  like  the  spinal  cord  in  its  internal  structure. 
The  region  of  the  medulla  leads  the  others  in  the  develop- 
ment of  the  nerve-paths. 


112 


PHYSIOLOGICAL  PSYCHOLOGY. 


In  the  spinal   cord,  the   posterior  roots  of  the  nerves 
appear  as  out-growths  of  a  series  of  median  cell-processes 

on  the  back  side  of  the 
cord.  Recent  discoveries 
indicate  that  the  motor- 
nerves  of  the  cord,  as 
well  as  of  the  brain,  arise 
from  the  fundamental 
plate. 

Development  of  the  An- 
terior Portions  of  theBrain, 
—  Further  details  con- 
cerning the  later  changes 
in  the  hind-brain  and  mid- 
brain  may  be  omitted. 
But  the  fate  of  the  an- 
terior portion  of  the  cere- 
bro-spinal  substance  re- 
quires a  brief  further 
description.  Of  its  two  divisions  (see  the  Table,  p.  Ill), 
the  posterior  (thalamen-cephalori),  is  at  first  a  simple  vesicle, 

formed  of  spin- 
dle-shaped cells 
with  walls  of 
nearly  uniform 
thickness.  Its 
floor  gives  rise 
to  the  optic 
chiasm  and  the 
optic  nerves;  its 
sides  become 
thickened  into 
the  optic  thala- 
mi ;  its  roof  gives 
rise  to  the  pineal  gland  and  surrounding  structures. 


FIG.  60.  —  Head  of  the  Embryo  of  a  Sheep,  cut 
through  the  middle.  3/i-  (Kolliker.)  u,  under 
jaw;  z,  tongue;  s,  septum  narium ;  occipitale 
basilare;  th,  thalamus  opticus;  vt,  roof  of  the 
third  ventricle;  cp,  posterior  commissure;  mh, 
mid-brain  divided  by  a  fold  into  two  parts;  /,  falx 
cerebri;/',  terminal  plate  of  the  fore-brain.  At 
the  prolongation  of  the  line  of  fm  is  the  foramen 
of  Monro.  t,  tentorium  cerebelli ;  cl,  cerebellum ; 
pi,  plexus  of  the  fourth  ventricle. 


FIG.  61.  — Brain  of  a  Six-months  Human  Embryo.  Natu- 
ral size.  (Kolliker.)  ol,  olfactory  bulb ;  fs,  fissure  of  Syl- 
vius; c,  cerebellum:  p,  pons  Varolii;  /,  flocculus;  o,  olive. 


DEVELOPMENT   OF   THE  NERVOUS   SYSTEM.  113 

The  larger  portion  of  the  development  from  the  anterior 
primary  vesicle  constitutes  the  rudiments  of  the  cerebral 
hemispheres.  Here  a  floor  and  a  roof  must  be  distin- 
guished. The  former  develops  into  the  striate  bodies  by 
the  thickening  of  its  walls.  The  latter  forms  the  hemi- 
spheres proper. 

One  principal  characteristic  of  the  mammals  is  the  early 
enlargement  of  the  cerebral  hemispheres.  In  the  human 
embryo  they  are  even  by  the  tenth  week  much  larger  than 
all  the  rest  of  the  brain.  They  grow  from  before  back- 
ward and  thus  cover  up,  one  after  the  other,  the  optic 
thalami,  corpora  quadrigemina,  and  cerebellum.  This 
physical  evolution  is  indicative  of  the  future  intellectual 
superiority  and  intellectual  growth  of  the  human  being. 
We  have  already  seen  how  early  and  significant  is  the 
formation  of  the  most  important  convolutions  and  fissures. 
By  the  end  of  the  seventh  month  of  embryonic  life,  the 
principal  features  of  the  cerebral  hemispheres  are  already 
definitely  fixed. 

Development  of  the  Eye. — Lateral  growths  of  the  brain- 
buds,  called  the  "optic 
vesicles  "  (see  p.  109), 
give  rise  to  the  ner- 
vous parts  of  the  eye.    • 

These     vesicles     are    g.          .  ^,  .t  \^^  ••  / 

originally    connected 

With  the  Sides  Of  the  FIG.  62.— Longitudinal  Sections  of  the  Eye  of  an 
fircst  PPrpHral  VPQiolp  Embryo,  in  three  stages.  (From  Remak.)  1,  com- 
mou  ucicuiai  vesicle  mencement  of  the  formation  of  the  lens  I,  by  depres- 
•i  -i  ,  -i  -I  sion  of  apart  of  A,  the  corneous  layer;  «,  r,  the  prim- 
by  Short  and  Wide  itive  ocular  vesicle  is  doubled  back  on  itself  by  the 

T  1                .1              , -i  depression  of  the  commencing  lens.    2,  the  depression 

S  t  a  1  KS  ;       tliey     "Mien  for  the  lens  is  now  enclosed,  with  the  lens  beginning 

I                                  •     -i   ,  to  be  formed  on  the  inner  side;   the  optic  vesicle  is 

Stand,    at    nenj^jy  rignt  more  folded  back.    3,  a  third  stage,  in  which  the  sec- 

,                 . ,                ,  ondary  optic  vesicle  g  I  begins  to  be  formed. 

angles  to  the  embryo. 

The  stalks  become  narrow  and  form  the  rudiments  of  the 
optic  nerves.  At  the  same  time  the  rudiments  of  the 
retina  are  formed  from  the  vesicles  themselves. 


114  PHYSIOLOGICAL   PSYCHOLOGY. 

The  bulb  of  the  optic  vesicle  is  then  made  into  a  cup  by 
doubling  it  upon  itself.  The  lens  of  the  eye  is  formed  by 
thickening  some  of  the  superficial  epiblast  and  involuting 
it  inward  over  the  front  of  the  optic  cup  (see  Fig.  62). 
This  involution  has  at  first  the  form  of  a  pit ;  then  of  a 
closed  sac  with  thick  walls ;  then  of  a  solid  mass.  The 
subsequent  development  of  the  eye  depends  upon  the  fact 
that  the  walls  of  the  optic  cup  grow  more  rapidly  than 
does  the  lens,  and  that  their  growth  does  not  take  place 
equally  in  all  portions  of  the  cup. 

The  different  layers  of  the  retina  are  formed  by  differen- 
tiations of  the  anterior  wall  of  the  hind  portions  of  the 
optic  cup.  Here  the  cells  multiply  rapidly,  and  undergo 
important  changes  while  the  wall  is  thickening.  In  its 
early  development  this  wall  resembles  the  brain  in  its 
structure.  It  may,  indeed,  be  considered  as  a  part  of  that 
organ. 

Development  of  the  Ear.  —  The  organ  of  hearing  originally 
appears  on  either  side  of  the  hind-brain  as  an  involution 
of  the  external  epiblast,  sunk  in  a  mass  of  mesoblast.  It 
is  then  shaped  as  a  slallow  pit  with  a  wide-open  mouth. 
As  the  mouth  closes  up,  the  pit  becomes  a  vesicle,  the  otic 
vesicle.  The  walls  thicken,  and  the  cavity  enlarges.  Its 
shape  becomes  triangular,  with  the  apex  of  the  triangle 
directed  inward  and  downward.  This  apex  is  elongated 
into  the  cochlear  canal.  Part  of  the  vesicle  is  stretched 
out  into  a  long  narrow  process  (recessus  vestibuli),  and 
from  the  wall  of  the  main  body  protuberances  grow  which 
become  the  vertical  semicircular  canals.  Other  protu- 
berances are  stretched  out  and  curved  into  ^ther  parts  of 
the  organ. 

The  cochlear  canal  is  further  elongated  and  curved. 
When  it  has  reached  two  and  a  half  coils,  the  thickened 
epithelium  of  its  lower  surface  forms  a  double  ridge,  from 
which  the  Organ  of  Corti  is  developed. 

Histogenetic   Development   of  the   Nervous   System.  —  All 


DEVELOPMENT   OF   THE   NERVOUS    SYSTEM.  115 

the  coarser  differentiations  of  structure  which  have  been 
described  are  but  the  expression,  as  it  were,  of  secret  and 
exceedingly  minute  changes,  called  "  histogenetic."  Deli- 
cate threads  of  nervous  tissue  have  been  laid  down,  and 
nerve-cells  have  been  propagated  {proliferated)  along  defi- 
nite lines.  The  white  matter  of  the  spinal  cord  first  appears 
in  four  patches  at  the  front  and  back  of  either  half.  The 
individual  fibres  appear  like  small  dots  in  these  patches. 
The  gray  matter  is  formed  by  differentiation  of  the  principal 
mass  of  the  walls  of  the  medullary  canal.  The  outer  cells 
lose  their  epithelial  character,  and  become  converted  into 
true  nerve-cells,  with  nerve-fibres  as  prolongations.  The 
nerve-fibres  remain  for  a  considerable  time  without  the 
medullary  sheath. 

The  early  histogenetic  development  of  the  brain  back 
of  the  cerebral  hemispheres  is  very  like  that  of  the  spinal 
cord.  In  the  floor  a  superficial  layer  of  delicate  nerve- 
threads  is  early  formed.  In  the  fore-brain  the  walls  of  the 
hemispheres  become  divided  into  two  layers,  the  inner  of 
which  unites  with  the  fibres  of  the  crura  cerebri  to  give 
rise  to  most  of  the  white  matter  of  Jie  hemispheres.  The 
outer  layer  of  rounded  cells  becomes  further  differentiated, 
the  deeper  part,  with  its  multiplication  of  numerous  cells, 
forming  the  principal  mass  of  the  gray  matter  of  the 
cortex. 

Thus  does  the  impregnated  ovum,  by  a  process  of  evolu- 
tion, become  developed  into  that  wonderful  complexity  of 
organs  which  constitutes  the  body  of  the  human  child.  Of 
the  correlated  psychical  development  of  the  embryo  little 
or  nothing  of  a  scientific  character  can  be  known.  But  the 
physical  process  by  which  the  nervous  mechanism  comes 
into  being  is,  nevertheless,  suggestive  for  the  student  of 
physiological  psychology.  To  some  of  the  conjectures 
and  speculations  which  legitimately  follow  from  our  still 
meagre  knowledge  of  human  embryology,  we  shall  return 
at  another  time. 


CHAPTER   V. 

GENERAL  PHYSIOLOGY  OF  THE  NERVES. 

THE  question,  What  can  Nervous  Substance  do?  natu- 
rally follows  the  consideration  of  its  chemical  and  formal 
constitution.  An  answer  to  this  question,  however,  can- 
not be  gained  by  inference  from  our  knowledge  of  the 
anatomy  and  histology  of  the  nervous  system.  It  is  only  by 
indirect  processes  of  observation  and  experiment,  combined 
with  no  little  conjecture,  that  even  the  beginnings  of  a 
clear  scientific  conception  of  the  functions  of  this  system 
can  be  found.  The  attainments  of  science  on  this  subject 
may  conveniently  be  stated  under  two  heads,  preceded 
by  a  brief  introduction.  We  consider  then,  first,  certain 
modes  of  activity  belonging  to  all  nervous  matter  as  such ; 
and,  second,  —  with  more  of  detail,  —  the  "  Nerves  as 
Conductors,"  and  the  "Automatic  and  Reflex  Functions 
of  the  Central  Organs." 

Functions  of  the  Nervous  Elements,  —  Nerves  and  nerve- 
cells  have  certain  properties  in  common;  within  certain 
limits  both  can  do  the  same  things.  These  properties  may 
perhaps  be  summed  up  in  the  two  words  Excitability  (or 
"irritability")  and  Conductivity.  Both  are  capable  of 
becoming,  under  the  action  of  stimuli,  the  subjects  of  a 
specific  kind  of  molecular  motion  called  "  neural."  When 
stimulated  or  irritated,  they  originate,  as  a  unique  func- 
tion, the  process  which  may  be  called  "  nerve-commotion." 
But  both  nerve-fibres  and  nerve-cells  can  also  propagate 
this  peculiar  kind  of  molecular  agitation  from  point  to 
point ;  they  can  conduct  nerve-commotion. 

116 


GENERAL   PHYSIOLOGY   OF  THE  NERVES.  117 

Nerve-commotion  is  never,  of  course,  an  uncaused  event. 
The  causes  that  excite  or  irritate  the  nervous  elements 
to  exercise  their  peculiar  function  are  called  " stimuli" 
Stimuli  are  of  two  kinds,  external  and  internal.  The 
former  comprise  all  such  modes  of  energy  as  excite  nerve- 
commotion  by  acting  on  the  peripheral  parts  of  the  ner- 
vous system,  —  the  terminal  nerve-fibrils  or  end-organs  of 
sense.  Internal  stimuli  act  directly  upon  the  substance 
(nerve-cells)  of  the  central  organ ;  they  consist  in  general 
of  changes  in  the  blood-supply, — increased  or  decreased 
oxygen,  presence  of  drugs,  etc. 

General  Office  of  the  Nervous  System,  —  In  all  forms  of 
animal  life,  except  the  lowest,  the  action  of  the  nervous 
system  constitutes  a  chief  characteristic  of  their  difference 
from  all  forms  of  plant  life.  Plants  as  well  as  animals 
have  contractile  tissue ;  but  the  former  never  have  nervous 
tissue,  not  to  say,  a  nervous  system.  The  unique  functions 
of  this  system,  as  possessed  by  all  the  higher  animals,  can 
perhaps  best  be  summed  up  in  the  one  word,  "concate- 
nation." The  linking,  or  chaining  together  —  as  it  were  — 
of  distant  and  different  physical  organs  and  systems,  and 
of  the  action  of  the  other  parts  of  the  body  with  the 
phenomena  of  psychical  life,  is  the  unique  function  of  the 
nervous  mechanism. 

In  the  plant,  for  example,  every  part  acts  directly  and 
slowly  upon  contiguous  parts  only,  for  the  effecting  of 
those  changes  upon  which  its  life  and  growth  depend. 
But  in  the  case  of  the  animal,  by  the  mediation  of  the 
nervous  system,  an  effect  produced  in  one  part  of  the 
body  may  make  itself  quickly  felt  in  every  other  part. 
A  draught  of  cold  air,  for  example,  strikes  some  portion 
of  the  surface  of  the  body.  Immediately,  the  heart  and 
lungs  modify  their  action ;  the  muscles  contract ;  the  secre- 
tions are  disturbed ;  a  shudder  runs  through  the  body ; 
and  perhaps  the  mind  is  seized  with  a  vague  feeling  of 


118  PHYSIOLOGICAL  PSYCHOLOGY. 

fear.  Thus  changes  which  involve  the  tissues  and  func- 
tions of  almost  all  the  organs  of  the  body  are  accomplished 
by  the  mediation  of  the  nervous  system. 

MORE  PARTICULAR  FUNCTIONS  OF  ALL  NERVES. 

We  have  already  seen  (p.  32  f .)  that  the  plan  on  which 
the  nervous  system  develops  leads  to  a  threefold  economy 
of  organs.  In  this  threefold  economy,  the  office  of  con- 
ducting the  nerve-commotion  between  the  end-organs  and 
the  central  organs  has  been  assigned  especially  to  the  nerves. 
The  function  of  conducting  neural  molecular  agitations 
belongs,  indeed,  as  an  essential  function,  to  all  nervous 
substance.  But  the  nerve-fibres,  as  bound  together  into 
nerves,  possess,  in  all  normal  conditions  of  the  nervous 
system,  this  office  pre-eminently.  Moreover,  it  is  only  as 
exercised  by  the  nerves  that  the  laws  of  neural  conduction 
can  be  at  all  satisfactorily  examined  by  direct  experiment. 

Physiological  Distinctions  in  the  Nerves.  —  If  we  considered 
only  the  different  effects  produced  by  conducting  nervous 
processes  along  the  different  nerves,  we  should  be  com- 
pelled to  divide  the  nerves  into  a  variety^of  classes.  In 
this  way  it  has  been  proposed  to  distinguish  "  nerves  of 
motion,"  "  nerves  of  inhibition  "  (or  check  upon  the  action 
of  other  nerves),  "  nerves  of  secretion,"  "  nerves  of  nutri- 
tion" (trophic  nerves),  "centripetal  nerves  that  have  no 
sensory  function,"  and  "sensory  nerves,"  whose  irritation 
may  result  in  conscious  sensation. 

The  question  arises  at  once,  however,  whether  the  differ- 
ent obvious  results  which  follow  irritating  all  these  nerves 
are  due  to  real  differences  in  the  functions  of  the  nerves 
themselves,  or  to  differences  in  the  structures  and  connec- 
tions where  the  nerves  terminate.  We  do  not  consider  the 
electrical  current  which  passes  along  different  wires  essen- 
tially different,  because  it  may  be  used  to  write  a  message, 
light  a  jet,  ring  a  bell,  or  cause  the  legs  of  a  frog  to  twitch. 


GENERAL   PHYSIOLOGY   OF   THE   NERVES.  119 

For  reasons  which  need  not  be  mentioned,  it  has  been 
customary  to  reduce  all  possible  classes  of  nerves  to  two, 
according  to  the  direction  in  which  they  perform  the  ser- 
vice of  conduction.  Those  nerves  which  conduct  nerve- 
commotion  outward  from  the  nervous  centres  are  called 
"efferent,"  or  "centrifugal,"  or  "motor."  Those  nerves 
which  conduct  nerve-commotion  inward  toward  the  ner- 
vous centres  are  called  "afferent,"  or  "centripetal,"  or 
"  sensory." 

Afferent  and  Efferent  Nerves,  —  The  attempt  has  further 
been  made  to  reduce  the  two  foregoing  kinds  of  nerves  to 
one  class.  It  is  properly  claimed  that  a  difference  in  direc- 
tion does  not  necessarily  prove  an  essential  difference  in 
function.  In  favor  of  such  a  difference,  however,  it  has 
been  urged  that  heat  is  a  stimulus  of  afferent  but  not  of 
efferent  nerves ;  and  that  a  constant  current  passing  along 
an  efferent  nerve,  so  long  as  there  are  no  sudden  changes 
in  its  strength,  does  not  make  the  attached  muscle  con- 
tract, while  such  a  current  does  seem  to  excite  impulses  in 
a  sensory  nerve. 

On  the  other  hand,  the  rate  of  conduction  in  both  kinds 
of  nerves  seems  to  be  about  the  same ;  and,  indeed,  most 
of  the  laws,  to  which  we  are  about  to  call  attention,  apply, 
essentially  unchanged,  to  both.  It  may  further  be  urged 
that  even  more  marked  differences  than  those  referred  to 
above  can  be  accounted  for  by  the  differences  in  the  sources 
of  the  stimulation.  A  molecular  disturbance,  which  would 
be  quite  powerless  to  stir  the  sluggish  muscle-fibres  when 
transmitted  to  them  by  a  motor-nerve,  might  occasion  pro- 
found changes  in  the  sensitive  ganglion-cells  of  the  central 
organ  when  transmitted  to  this  organ  by  a  sensory  nerve. 

Various  attempts  have  been  made,  more  or  less  success- 
fully, to  demonstrate  by  experiment  that  motor  and  sen- 
sory nerves  can  be  made  to  discharge  each  other's  functions. 
Some  experimenters  have  succeeded  in  uniting  the  central 


120  PHYSIOLOGICAL  PSYCHOLOGY. 

end  of  the  sensory  nerve  of  the  dog's  tongue  with  the 
peripheral  end  of  the  motor  nerve,  on  the  same  side. 
Others  have  reversed  the  course  of  the  nerve-fibres  in  the 
tail  of  a  rat,  by  bending  this  appendage  over,  and  planting 
its  end  in  the  back.  If  these  experiments  are  not  quite 
satisfactory,  those  of  Kiihne  may  fairly  be  said  to  be  con- 
clusive. He  showed  that  if  we  divide  the  broad  end  of  the 
sartorius  muscle  of  the  frog  into  a  forked  shape,  the  same 
stimulation  will  ascend  the  fibrils  of  one  tine  of  the  divided 
muscle,  and  descend  the  fibrils  of  the  other  tine. 

No  good  reason  appears,  then,  why  we  should  not  con- 
sider all  nerves  as  essentially  alike  in  their  powers  of 
conduction.  It  is  upon  this  assumption  that  the  science  of 
so-called  "  General  Nerve-Physiology "  is  built  up  exper- 
imentally. In  building  up  this  science,  the  efferent  nerves 
of  frogs  have  been  chiefly  used  for  purposes  of  experiment. 
A  preparation  of  such  a  nerve  with  a  muscle  attached  is 
the  subject  whose  behavior  is  investigated. 

The  Nerve-Muscle  Preparation.  —  The  most  convenient 
form  of  machine  for  experiment  in  "general  nerve-phys- 
iology" requires  a  freshly  dissected  (cjastrocnemius  or  other) 
muscle  of  a  frog  with  the  attached  (sciatic  or  other)  nerve. 
Such  a  preparation  can  be  kept  alive  for  some  time  in  a 
cool  moist  chamber.  By  the  simple  contrivance  of  connect- 
ing the  end  of  the  muscle  with  a  lever,  arming  the  lever 
with  some  means  of  making  a  mark  (pen,  bristle,  or  needle), 
and  bringing  its  point  to  bear  on  a  travelling  surface  (plain 
or  smoked  paper,  or  glass),  the  time  and  amount  of  the 
contractions  of  the  muscle  maybe  recorded.  Stimulation 
may  be  accomplished  with  any  kind  of  irritant,  but  for 
obvious  reasons  the  electrical  current  is  preferable  as  a 
rule.  It  may  be  applied  under  the  greatest  variety  of 
conditions,  and  to  any  point  in  the  nerve,  and  with  any 
degree  of  intensity. 

The  line  traced  by  the  armed  end  of  the  lever,  as  it  rises 


GENERAL  PHYSIOLOGY  OF  THE  NERVES.      121 

and  falls  with  the  contractions  of  the  muscle,  is  called  the 
"  muscle-curve."  This  curve  is  a  measure  of  the  observ- 
able effect  produced  by  irritating  the  nerve.  If  the  elec- 
trical current  flows  with  the  course  of  the  nerve  toward 
the  muscle,  it  is  called  "  descending,"  or  direct ;  if  it  flows 
in  the  opposite  direction,  it  is  "ascending,"  or  inverse. 
The  movement  of  the  muscle  which  follows  closing  of  the 
current  is  called  the  "making  contraction,"  or  "closing 
contraction";  that  which  follows  its  opening  is  called  the 
"  breaking  contraction,"  or  "  opening  contraction."  When 
the  single  stimulations  are  repeated  with  sufficient  rapidity, 
the  spasms  fuse  into  one  prolonged  effort  of  the  muscle, 
known  as  "  tetanus,"  or  "  tetanic  contraction."  The  nerve 
may  then  be  said,  with  the  muscle,  to  be  "  tetanized." 

CONDITIONS  OF  .THE  FUNCTIONS  OF  NERVES. 

Of  the  conditions  under  which  alone  the  nerves  are 
capable  of  exercising  their  functions  the  most  important 
are  the  following  three  :  — 

(1)  Vitality  of  the  Nerves.  —  A  nerve  cannot  act  as  the 
conductor  of  a  nerve-commotion  unless  it  is  alive.  The 
process  of  conduction  is  not  therefore  merely  mechanical, 
like  that  of  electricity  along  a  wire,  but  is  physiological 
and  vital.  The  death  of  the  nerve  is  not,  however,  simul- 
taneous with  that  of  the  body  from  which  it  is  taken,  or  of 
the  muscle  to  which  it  is  attached.  On  the  contrary,  by 
careful  treatment,  it  may  be  preserved  alive  for  some  time 
after  excision.  Since  the  nerve,  unlike  the  muscle,  has  no 
death-rigor,  it  is  difficult  to  say  precisely  when  it  is  dead. 
The  existence  of  electrical  phenomena  in  the  nerve  for 
some  time  after  it  has  ceased  to  excite  the  muscle  is 
thought  by  some  authorities  to  show  its  continued  vitality. 

Nerves,  when  dying,  exhibit  two  marked  changes  of 
excitability.  Immediately  after  being  cut,  the  excitability 
of  the  nerve  increases,  and  afterward  sinks  to  zero  by  sue- 


122  PHYSIOLOGICAL  PSYCHOLOGY. 

cessive  stages  of  diminution.  The  course  of  these  changes 
is  different  for  different  portions  of  its  length.  Again,  the 
lower  portion  of  the  cttt^nerve  seems  to  preserve  a  given 
degree  of  vitality  for  the  longest  time.  Hence  "Valli's 
principle:  Nerves  die  from  the  centr&Jo  the  periphery. 

Closely  allied  to  the  foregoing  changes  are  those  which 
take  place  when  the  cut  nerve  remains  in  its  place  in  the 
living  animal  organization  (in  situ).  For  such  a  nerve 
the  law  of  increased  irritability  immediately  after  section 
seems,  in  most  cases,  to  hold  good ;  the  application  can  be 
tested,  however,  only  in  the  case  of  motor  nerves.  Nerves, 
cut  in  situ,  lose  their  vitality  after  a  time  —  in  warm- 
blooded animals,  of  three  or  four  days,  but  in  cold-blooded, 
of  a  week  or  more.  A  fatty  or  granular  degeneration 
(discovered  by  Waller  in  1850)  takes  place  in  nerve-fibres 
that  are  severed  from  the  central  organ ;  and  this  degener- 
ation proceeds  from  the  place  of  section  to  the  extreme 
peripheral  portion  of  the  fibre.  A  cut  nerve  remaining  in 
situ  may  be  regenerated  by  the  axis-cylinders  growing  out 
of  the  central  portion  and  running  into,  and  between,  the 
sheaths  of  Schwann  of  the  peripheral  portion.  According 
to  some  authorities  the  conductivity  of  the  nerve  is  then 
regained  earlier  than  its  power  of  local  irritability. 

(2)  Use  of  Oxygen  by  the  Nerves,  —  As  compared  with 
the  end-organs  and  the  central  organs,  or  even  with  the 
muscles,  the  nerves  are  relatively  independent  of  the  pres- 
ence of  oxygen  for  the  exercise  of  their  physiological  func- 
tion.    The  irritability  of  the  nerves  continues  almost  as 
long  in  a  moist  vacuum,  or  in  indifferent  gases,  as  in  the 
air.     It  may  be  argued,  however,  from  the  marked  depend- 
ence of  nervous  tissue,  in  general,  upon  a  supply  of  arte- 
rial blood,  as  well  as  from  the  general  mechanical  theory 
of  the  nervous  system,  that  some  oxygen  is  an  essential 
condition  of  the  activity  of  the  nerves. 

(3)  Recovery  from  Exhaustion.  —  The  nerves,  when  "  ex- 


GENEKAL   PHYSIOLOGY   OF   THE   NERVES.  123 

hausted  "  —  as  it  is  said  —  cannot  perform  their  physiologi- 
cal functions.  But  exhaustion  of  the  nerves  is  difficult  to 
distinguish  from  exhaustion  of  the  central  organs  or  of  the 
end-organs.  In  the  case  of  the  nerve-muscle  machine 
Bernstein  thinks  he  has  shown  that  by  far  the  greater  part 
of  the  effects  of  prolonged  and  severe  stimulation  is  due 
to  the  rawscfo-element  in  the  machine;  and  that  exhaus- 
tion in  the  nerve  comes  on  much  more  slowly  than  in  the 
muscle.  Indeed,  some  have  gone  so  far  as  to  hold  that  the 
nerve  is  not  exhausted  at  all,  but  resembles  in  this  regard 
a  metallic  wire.  But  more  recent  researches  seem  to 
show  —  as  indeed  we  should  expect  on  grounds  of  general 
theory  —  that  a  prolonged  tetanizing  current  may  fatigue 
the  nerve,  even  when  the  end-apparatus  continues  able  to 
perform  its  functions.  Ordinarily,  however,  when  we  are 
tired  nervously,  it  is  the  central  organs,  or  end-organs, 
rather  than  the  conducting  nerves,  that  are  tired. 

PHYSICAL  PROPERTIES  OF  THE  NERVES. 

The  phenomena  called  forth  by  irritating  a  nerve  depend 
upon  the  character,  amount,  and  method  and  place  of 
application,  of  the  stimuli  employed.  This  dependence 
suggests  certain  truths  as  to  the  physical  properties  of  the 
nerves  as  conductors. 

Mechanical  Properties  of  the  Nerves.  —  The  elasticity, 
ductility,  cohesion,  etc.,  of  nerves  are  of  little  interest  to 
the  student  of  physiological  psychology.  More  pertinent 
is  the  fact  that  all  kinds  of  mechanical  attacks  upon  the 
nerves  excite  them,  and  are  followed  by  pain  in  case  of 
the  sensory  nerves,  and  by  contraction  in  the  case  of  motor 
nerves.  Tetanus  may  be  produced  with  a  toothed  wheel 
or  hammer.  A  certain  suddenness  of  the  shock  seems 
necessary  to  excite  the  nerve.  Pressure  on  a  nerve  may 
be  gradually  increased  until  its  power  of  conductivity  is 
lost,  without  exciting  it.  Slight  pressure  or  traction 


124  PHYSIOLOGICAL  PSYCHOLOGY. 

seems  to  increase  the  irritability  and  speed  in  conduction 
of  the  nerve.  Yet  nerves  may  be  cut  so  suddenly  as  not 
to  excite  them. 

Thermic  Properties  of  the  Nerves.  —  Little  is  known  as  to 
the  specific  heat  of  nerves,  or  as  to  their  power  to  conduct 
heat.  But  the  effect  of  heat  on  the  function  of  these  organs 
is  very  marked.  The  results  of  experiment  differ  as  to  the 
degree  of  heat  which  will  act  as  a  stimulus  upon  the 
nerves.  Considerable  changes  in  the  medium  temperatures 
appear  to  have  no  effect.  One  investigator  found  that 
suddenly  warming  a  nerve  to  about  35°- 40°  C.  occasioned 
a  spasm  in  the  attached  muscle ;  and  warming  to  a  higher 
degree  produced  tetanic  convulsions.  Long  ago  that  noted 
authority,  E.  H.  Weber,  showed  that  heat  and  cold  do  not 
produce  sensations  when  applied  directly  to  the  sensory 
nerve-trunks  in  man.  For  this  peculiar  sensory  effect  the 
intervention  of  end-organs  seems  necessary. 

Four  periods  have  recently l  been  distinguished  in  the 
effects  produced  by  heat  upon  the  irritability  of  the  motor 
nerve.  These  are  thus  described :  ( A)  Gradual  increase 
to  a  maximum  of  irritability,  —  viz.  32.75°-39.25°  C. ; 
(^)  then  gradual  diminution  of  irritability  to  its  total  loss  ; 
((7)  condition  of  no  irritability,  a  period  coming  at  any 
point  within  5°  above  the  temperature  of  maximum  con- 
traction ;  and  finally  (D)  development  of  heat-rigor. 

Warmth  increases  the  immediate  expenditure  of  energy 
in  an  excised  nerve,  and  so  hastens  its  death ;  cold  delays 
this  expenditure  and  so  conserves  the  nerve. 

Chemical  Properties  of  the  Nerves.  —  The  effect  of  most 
chemical  agents  on  the  nerve  is  to  destroy  without  exciting 
it.  Changes  of  the  amount  of  water  in  the  substance  of 
the  nerve  affect  its  functional  activity.  A  slight  drying 
raises  its  irritability;  and  drying  also  produces  contrac- 

1  By  Charles  L.  Edwards,  in  Johns  Hopkins  Studies  from  the  Bio- 
logical Laboratory,  June,  1887. 


GENERAL  PHYSIOLOGY  OF  THE  NEKVES.     125 

tions  ending  in  tetanus.  Swelling  the  nerve  decreases  its 
irritability  to  the  point  of  entire  loss.  Certain  acid  and 
alkaline  solutions  also  affect  the  nerve  very  much  like 
drying  it.  Some  organic  substances,  like  urea,  sugar,  and 
glycerine,  irritate  the  nerve.  The  principle  seems  to  be, 
that  all  chemical  stimulation  of  the  nerves  is  closely  con- 
nected with  the  destruction  of  the  nervous  tissue. 

Electrical  Properties  of  the  Nerves.  —  The  resistance  of 
living  nerves  to  the  electrical  current  is  probably  about 
the  same  as  that  of  the  muscles;  it  has  been  given  at 
50,000,000  times  that  of  copper  wire.  The  conductivity 
of  the  nerve  has  also  been  given  as,  on  the  average,  14.86 
times  that  of  distilled  water. 

The  excitatory  effect  of  the  constant  current  upon  the 
nerves  follows  the  principle  stated  by  that  great  explorer, 
du  Bois-Reymond,  in  1845.  This  effect,  as  measured  by 
the  contraction-curve  of  the  muscle,  does  not  correspond 
to  the  absolute  value  of  the  intensity  of  the  current  at  each 
moment,  but  to  the  change  in  this  value  from  moment  to 
moment ;  and  the  effect  is  greater  the  less  the  time  in 
which  changes  of  the  same  magnitude  in  the  current 
occur,  or  the  greater  their  magnitude  in  the  same  length 
of  time.  The  essential  fact  is  that  constant  currents, 
while  they  remain  constant,  do  not  irritate  the  nerve; 
variations  in  these  currents  do  irritate  it. 

Even  upon  the  sensory  nerves  it  is  not  certain  that  the 
constant  current  itself,  apart  from  changes  in  its  strength, 
can  have  much  excitatory  effect.  The  sensory  experiences 
which  follow  such  a  current  are  chiefly  due  to  changes 
induced  in  the  end-organs  and  central  organs. 

Excitatory  Effect  of  the  Constant  Current.  —  If  we  experi- 
ment with  the  electrical  current  upon  a  nerve  we  find  that 
its  excitatory  effect  is  dependent  upon  the  direction  in 
which  the  current  flows.  The  following  table,  by  Pfliiger, 
gives  the  results  reached  by  a  large  number  of  observers:  — 


126 


PHYSIOLOGICAL   PSYCHOLOGY. 


ASCENDING  CURRENT. 

DESCENDING  CURRENT. 

STRENGTH  or 

CURRENT. 

Making. 

Breaking. 

Making. 

Breaking. 

Weak  .... 

Contraction 

Rest 

Contraction 

Rest. 

Medium.  .  . 

Contraction 

Contraction 

Contraction 

Contraction. 

Strong.  .  .  . 

Rest 

Contraction 

Contraction 

Rest  or  weak 

Contraction. 

The  most  important  point  in  this  table  is  more  clearly 
brought  out  by  the  following  recent  summary 1  of  results  : 
"  Up  to  a  certain  strength  of  current  a  stimulus  will  give 
contraction  when  the  cathode  lies  next  to  the  muscle  (i.e. 
the  current  is  descending),  which  will  give  no  contraction 
when  the  anode  is  in  that  position  (current  ascending). 
Above  this  strength  the  reverse  holds,  and  a  stimulus 
which  is  followed  by  contraction  when  the  excitation  has 
to  pass  the  anode,  evokes  no  response  when  it  has  to  pass 
the  cathode." 

The  excitatory  effect  of  the  electrical  current  upon  the 
nerve  is  also  dependent  upon  the  strength  of  the  current. 
It  increases  with  the  strength,  from  the  lowest  observable 
point,  until  it  soon  reaches  a  maximum ;  after  this,  further 
increase  of  the  effect  of  the  current  is  to  be  recognized 
only  by  the  expanding  of  this  condition  of  higher  irrita- 
bility—  called  "  electrotonus  "  —  over  the  extra-polar  parts 
of  the  nerve. 

The  effect  of  the  current  upon  the  nerve  also  depends 
upon  the  length  of  nerve  excited,  and  upon  the  angle  at 
which  the  stimulus  is  applied.  Up  to  a  certain  limit  — 
fixed  by  different  investigators  at  from  -^  to  ^  inch  —  the 
excitatory  effect  increases  with  the  length  of  the  nerve 
through  which  the  current  flows.  The  electrical  current 

1  An  Article  by  G.  N.  Stewart,  in  Journal  of  Physiology,  Oct.,  1889. 


GENERAL  PHYSIOLOGY   OF   THE  NERVES.  127 

apparently  does  not  excite  the  nerve  at  all  when  it  flows 
through  it  precisely  at  right  angles  to  the  nerve's  axis. 

The  duration  of  the  current  also  influences  its  effect  as 
a  stimulus.  It  would  appear  that  the  current  must  act 
upon  the  nerve  for  at  least  about  O.OOli  of  a  second  in 
order  to  excite  it.  By  cooling  the  nerve  this  "  sluggish  " 
period  may  be  increased  to  nearly  0.02  of  a  second.  In 
ordinary  circumstances,  however,  it  is  thought  that  the 
action  of  the  stimulus  for  0.017-0.018  second  will  cause 
the  muscles  to  contract  as  much  as  the  same  strength  of 
current  when  constantly  applied. 

Electrotonus  of  the  Nerves.  —  When  the  nerve  of  a  nerve- 
muscle  machine  is  under  the  influence  of  a  constant  cur- 
rent of  electricity,  very  important  changes  in  its  condition 
are  observed,  as  respects  both  its  excitability  and  its  con- 
ductivity. The  general  fact  that  such  changes  are  pro- 
duced as  the  effect  of  applying  the  constant  current  is 
undoubted.  But  the  precise  nature  of  some  of  these 
changes  is  disputed ;  while  no  theory  has  as  yet  been  de- 
vised which  will  satisfactorily  account  for  them  all.  We 
shall  confine  our  account  at  present  to  the  briefest  possible 
statement  of  the  more  important  alleged  facts  ;  any  refer- 
ence to  theory  which  seems  desirable  at  all,  will  be  made 
in  another  connection. 

The  changed  condition  of  a  nerve,  as  respects  its  phys- 
iological function,  which  is  produced  in  it  by  a  constant 
electrical  current,  is  called  "Electrotonus."  "Pfliiger's 
law,"  so-called,  states  the  case,  in  general,  as  follows  :  The 
excitability  of  a  nerve  under  the  action  of  the  constant  cur- 
rent is  increased  in  the  catelectrotonized  region  (that  is,  on 
both  sides  of  the  cathode,  or  negative  electrode,  —  the 
point  where  the  current  leaves  the  nerve),  and  diminished 
in  the  anelectrotonized  region  (that  is,  on  both  sides  of  the 
anode,  or  positive  electrode,  —  the  point  where  the  current 
enters  the  nerve).  This  law  is  said,  by  a  chief  modern 


128  PHYSIOLOGICAL  PSYCHOLOGY. 

authority,  to  hold  good  of  all  kinds  of  stimulus,  and  in 
all  cases. 

The  electrotonic  effect  of  the  constant  current  upon  the 
nerve,  like  its  direct  excitatory  effect,  is  influenced  by  the 
strength  of  the  current,  by  its  direction,  its  making  and 
breaking,  and  by  the  length  of  the  nerve  through  which 
the  current  flows.  The  changes  called  "  electrotonic " 
occur  in  the  region  of  the  negative  pole  (cathode)  imme- 
diately upon  making  the  current;  they  then  quickly  but 
slightly  increase  and  afterwards  fall  off  more  slowly  again. 
In  the  region  of  the  positive  pole  (anode)  the  changed 
condition  develops  more  slowly  until  it  reaches  a  maxi- 
mum, and  then  gradually  diminishes. 

Recent  researches  have  led  some  investigators  to  hold 
that  the  conductivity  of  the  nerve  is  changed  by  the  con- 
stant current  in  a  different  manner  from  its  excitability. 
In  its  electrotonic  condition —  that  is  to  say — the  conduc- 
tivity of  the  nerve  is  found  to  be  less  around  the  cath- 
ode than  around  the  anode.  From  this  the  conclusion  is 
drawn  that  the  origin  of  the  process  of  excitation  of  the 
nerve  is  not  like  its  propagation.  Into  the  refinements  of 
this  change,  when  the  stimulus  of  the  electrical  current  is 
applied  to  different  parts  of  the  nerve  outside,  or  within, 
the  poles  (inter-polar  and  extra-polar)  we  cannot  enter. 

PROCESSES  EVOKED  IN  CONNECTION  WITH  THE  FUNCTION 
OF  NERVES. 

When  the  nerve  is  excited  certain  processes  connected 
with  its  physiological  action  are  indicated,  in  a  more  or 
less  obvious  way. 

Mechanical  Processes  in  Excited  Nerves.  —  No  appreciable 
mechanical  changes,  like  the  contraction  of  the  muscle- 
fibre,  can  be  detected  in  excited  nerves.  Whatever  changes 
occur  are  invisible  and  impalpable.  In  the  nerve-cells, 
however,  mechanical  changes  can  be  detected  as  the  result 


GENERAL   PHYSIOLOGY    OF   THE   NERVES.  129 

of  excitation.  Repeated  and  prolonged  excitation  of  the 
ganglion-cells  of  the  posterior  root  results  in  shrinkage 
of  their  nucleus  and  of  the  cell-protoplasm  3  and  in  chang- 
ing the  nucleus  from  a  smooth  and  regular  to  a  jagged 
and  irregular  outline.  The  large  cells  show  most  of  this 
effect  of  being  obliged  to  do  work;  the  small  cells  little  or 
none  at  all.  The  average  shrinkage  of  the  large  cells  is 
found  to  be  measurable  as  —  in  some  cases  —  from  24  to 
36  per  cent.1 

Thermic  Processes  in  Excited  Nerves,  —  If  any  rise  of  tem- 
perature is  produced  in  a  nerve  by  irritating  it,  the  amount 
is  exceedingly  small.  Helmholtz  concluded  that  his  means 
of  detecting  heat  to  within  a  few  thousandths  of  a  degree 
showed  no  such  change  in  excited  nerves.  On  the  other 
hand,  nervous  excitation  appears  to  produce  a  perceptible 
change  of  temperature  in  the  centres  of  the  brain;  and 
this  change  can  scarcely  be  due  wholly  to  increased  flow 
of  arterial  blood.  But  to  this  subject  we  shall  return  in 
another  connection. 

Chemical  Processes  in  Excited  Nerves.  —  The  most  obvious 
indications  that  chemical  processes  are  concerned  in  the 
physiological  functions  of  excited  nerves  are  certain 
changes  in  "reaction,"  or  in  taking  stains,  which  some 
observers  claim  to  have  found.  It  has  been  asserted  that, 
after  extreme  exertion  caused  by  cramping  in  cases  of 
strychnine-poisoning,  the  nerves  have  an  acid  reaction. 
Very  recently  two  observers,  on  comparing  two  frogs,  one 
of  which  was  killed  after  resting  and  the.other  after  having 
the  eighth  nerve  stimulated  for  an  hour,  found  several  per 
cent,  more  nuclei  staining  red  in  the  stimulated  than  in 
the  rested  pair  of  nerves.  Evidences  of  marked  chemical 
changes  in  the  nervous  centres,  due  to  work  done  there, 
are  of  course  not  wanting.  But  the  direct  experimental 
evidence  for  the  same  thing  in  the  nerves  is  still  incomplete. 

1  See  the  American  Journal  of  Psychology,  May,  1888,  pp.  479  ff. 


130  PHYSIOLOGICAL  PSYCHOLOGY. 

Electrical  Processes  in  Excited  Nerves.  —  In  1843  du  Bois- 
Reymond  found  what  he  considered  direct  experimental 
proof  of  the  existence  of  electrical  currents  in  the  nerves. 
It  had,  of  course,  been  previously  conjectured  that  nerve- 
commotion  is  a  phase  of  electricity.  But  this  experi- 
menter discovered  that,  if  we  cut  a  nerve  and  then  apply 
an  electrometer  to  it,  the  cross-section  is  negative  toward 
the  longitudinal  surface  of  the  nerve.  The  current,  which 
is  thus  shown  to  be  flowing  in  the  nerve,  from  the  cut  end 
to  the  equator,  is  called  "natural  nerve-current,"  or  "current 
of  rest."  Its  electro-motive  force  is  greater,  the  larger  and 
thicker  the  nerve.  In  the  sciatic  nerve  of  a  frog  it  is  given 
at  from  0.022  to  0.046  of  a  Daniell's  cell.  It  continues  for 
some  time  after  the  irritability  of  the  nerve  is  lost. 

The  same  investigator  found  that  the  "  current  of  rest "  is 
diminished  in  energy  by  tetanizing  the  nerve.  This  swing 
of  the  needle  which  measures  the  "  current  of  rest,"  back- 
ward toward  zero  when  the  nerve  is  repeatedly  irritated  by 
passing  through  it  an  interrupted  current,  is  called  "  nega- 
tive variation."  It  shows  that  the  electro-motive  force  of 
the  nerve  is  diminished  by  the  nerve  being  excited. 

The  bearing  of  these  phenomena  also  upon  a  general 
mechanical  theory  of  the  nervous  system  will  be  referred 
to  in  other  connections. 

LAWS  OF  CONDUCTION  IN  THE  NERVES. 

Only  a  very  few  statements  can  be  made,  with  respect 
to  the  physiological  function  of  the  nerves  as  conductors, 
which  are  properly  entitled  to  the  dignity  of  being  called 
44  laws. "  And  these  laws  are  determined  almost  wholly  by 
experiments  with  the  motor  nerves  of  frogs.  There  is  evi- 
dence, however,  in  respect  to  certain  of  the  more  simple 
forms  of  activity,  that  all  nerves  conduct  nerve-commotions 
in  essentially  the  same  way. 

Relations  of  Magnitude  between  Stimulus  and  Result,  —  On 


GENEKAL   PHYSIOLOGY   OF   THE   NERVES.  131 

attempting  accurately  to  compare  the  amount  of  the  stim- 
ulus applied  to  the  nerves  with  the  amount  of  resulting 
nervous  impulse,  great  difficulties  are  encountered.  There 
is  indeed  no  absolute  measure  for  either  of  the  values  which 
it  is  desired  to  compare.  Electricity  is  the  only  stimulus 
of  the  nerves  that  admits  of  a  fairly  approximate  measure- 
ment by  objective  standards.  The  effect  produced  by 
stimulation  is  almost  wholly  manifested  in  organs  with 
which  the  nerve  is  connected,  rather  than  in  the  nerve 
itself.  It  does  not,  therefore,  admit  of  easy  direct 
measurement. 

Measuring  the  result  of  the  stimulus  in  the  nerve  by  the 
amount  of  contraction  produced  in  the  connected  muscle, 
we  find  it  to  be  (as  has  already  been  indicated,  see  p.  126) 
within  certain  limits,  directly  proportional  to  the  amount 
of  the  stimulus.  Two  remarkable  apparent  exceptions  to 
this  law  are  noted :  (1)  On  increasing  the  amount  of  the 
stimulus  beyond  the  point  necessary  to  produce  the  first 
maximum  contraction,  another  stage  is  reached  in  which 
the  effect  further  increases,  in  proportion  to  the  stimulus, 
until  a  second  maximum  is  gained.  (2)  In  some  circum- 
stances, after  reaching  the  first  maximum,  the  effect  dimin- 
ishes with  the  increase  of  the  stimulus,  then  rises  on  further 
increase  until  the  second  maximum  is  reached. 

The  excitability  of  the  different  nerves  is  different,  and 
of  different  localities  of  the  same  nerve  under  different 
circumstances.  It  is  usually  greater  in  winter  than  in 
summer.  In  the  cut  nerve  it  is  greater  near  the  cross- 
section.  The  reflex  effects  of  stimulating  a  sensory  nerve 
are  said  to  be  greater  the  nearer  the  central  organ  the 
stimulus  is  applied.  The  lower  part  of  a  nerve  is  found 
more  excitable  under  the  ascending,  the  upper  under  the 
descending,  induction-current. 

Summation  of  Stimulations  in  the  Nerves.  —  In  order  to 
keep  the  successive  waves  of  nerve-commotion  apart,  an 


132  PHYSIOLOGICAL   PSYCHOLOGY. 

interval  of  about  -j-J^  second  must  elapse  between  the  re- 
peated stimulations.  Otherwise  they  fuse,  and  tetanus 
results.  If  this  interval  is  observed,  the  combined  effects 
of  the  different  stimulations  may  be  piled,  or  "  summed  " 
up,  in  the  nerve.  They  may  then  be  seen  in  superimposed 
contractions  of  the  muscle.  This  law  is  also  important  for 
a  mechanical  theory  of  the  nervous  system. 

Speed  of  Nervous  Impulses.  —  In  1844  the  great  physiolo- 
gist Miiller  declared  it  forever  impossible  to  know  the 
speed  of  the  nervous  impulses.  In  1850  Helmholtz  an- 
nounced the  speed  as  from  26.4  meters  (86.6  feet)  to 
27.25  meters  in  motor  nerves.  Subsequent  researches 
have,  in  the  main,  confirmed  the  conclusion  of  Helmholtz. 
The  rate  of  nervous  impulses  varies  greatly,  however,, 
under  different  circumstances.  By  changes  in  temperature 
results  can  be  obtained  in  the  motor  nerves  of  man,  varying 
from  98  feet  to  295  feet  per  second.  The  general  conclu- 
sions for  the  sensory  nerves  favor  numbers  lying  between 
98  and  131  feet  per  second.  As  soon  as  the  strength  of 
the  stimulus  rises  above  a  certain  limit,  the  speed  of  the 
resulting  impulses  appears  to  increase  with  the  strength 
of  the  stimulus. 

In  the  spinal  cord  and  in  the  brain  the  speed  of  the  ner- 
vous impulses  is,  in  general,  much  slower  than  in  the 
peripheral  nerves.  This  is  due  to  the  far  greater  com- 
plexity of  these  organs,  and  to  the  accompanying  possibility 
of  the  impulses  spreading  into  side  tracts,  as  it  were :  in 
brief,  the  greater  variety  and  amount  of  the  work  that 
must  be  done.  Exner  calculated  the  speed  of  motor 
impulses  in  the  cord  at  11  to  15  meters  (about  36  to  49 
feet).  The  sensory  impulses  of  the  cord,  he  thought, 
travel  at  the  average  rate  of  about  8  meters  (about  26J 
feet).  Sensations  of  touch  arise,  as  we  all  know  by  expe- 
rience, later  than  sensations  of  pain,  when  we  are  struck 
with  a  missile,  or  burned  with  a  brand.  Some  have  main- 


GENERAL   PHYSIOLOGY   OF   THE  NERVES.  133 

tained,  therefore,  that  the  speed  of  the  former  is  to  that  of 
the  latter  as  from  27  to  50  meters  compared  with  8  to  14. 
The  argument  is  not  conclusive,  however,  since  we  do  not 
know  the  length  of  the  paths  by  which  the  impulses  that 
produce  the  two  kinds  of  feeling  travel,  or  the  kind  and 
amount  of  cerebral  action  which  they  respectively  involve. 

Integrity  of  the  Nerves  Necessary.  —  The  slightest  separa- 
tion of  the  parts  of  a  nerve,  even  if  its  cut  ends  are  left 
in  the  closest  mechanical  contact,  destroys  its  power  to 
conduct  nervous  impulses.  Nerve-commotion,  unlike  the 
electrical  current,  cannot  jump  the  smallest  gap  in  the  ner- 
vous structure.  The  ancients  knew  that  tying  a  nerve 
prevents  its  action.  They  explained  the  fact  by  saying 
that  the  flow  of  nervous  fluid  was  thus  hindered.  So  also 
does  the  fineness  of  the  localization  which  belongs  to  the 
organs  of  motion,  and  especially  to  the  organs  of  special 
senses,  like  the  skin  and  eye,  indicate  the  physiological 
isolation  of  the  nerve-fibre  during  its  course  between  the 
end-organs  and  the  central  organs.  It  would  further  seem 
that  the  law  of  the  "  specific  energy  "  of  each  nervous  ele- 
ment is  connected  with  the  assumption  necessary  to  explain 
the  phenomena  attendant  upon  the  starting  and  propagat- 
ing of  nervous  impulses  in  the  conducting  nerves.  But 
to  this  subject  of  the  "specific  energy"  of  the  nervous 
elements  we  shall  recur  at  another  time. 

When  speaking  of  conduction  in  the  nervous  substance 
of  the  spinal  cord  or  of  the  brain,  we  are  not  to  think  of  the 
nerve-commotion  as  moving  along  one  fixed  path,  after  the 
exact  analogy  of  the  far  simpler  case  of  the  nerve-muscle 
machine.  The  spinal  cord  does  not  act  as  a  "perfectly 
isomorphic  medium "  for  the  transmission  of  nervous 
impulses.  Its  extremely  complex  structure  has  shown  us 
that  it  is  not  adapted  to  act  as  such  a  medium.  The  case 
of  the  brain  in  this  regard  is  even  more  complicated. 
After  all  the  thousands  of  experiments  which  have  been 


134  PHYSIOLOGICAL  PSYCHOLOGY. 

performed  in  what  is  called  "nerve-physiology,"  we  are 
not  yet  in  a  position  even  to  indicate  with  scientific  exact- 
ness a  complete  mechanical  theory  of  those  molecular 
wave-like  disturbances  which  the  application  of  stimuli 
produces  in  a  single  nerve  attached  to  a  muscle.  How 
much  less  then  do  we  know  of  the  molecular  science  of 
the  nerve-commotions  in  the  cord  and  in  the  brain  ?  Yet 
that  the  nerve-commotions  are  molecular  wave-like  changes 
there  can  be  no  doubt.  And  these  changes  are  connected 
with,  but  are  not  identical  with,  those  mechanical,  ther- 
mic, chemical,  and  above  all,  electrical  processes,  which 
have  just  been  described. 


CHAPTER  VI. 
REFLEX  AND  AUTOMATIC  NERVOUS  FUNCTIONS. 

WHEN  a  physiological  function  is  occasioned  in  some 
peripheral  nerve,  independently  of  a  so-called  act  of  will, 
by  the  stimulation  of  some  other  peripheral  nerve,  this 
function  is  said  to  be  "reflex."  In  other  words,  reflex 
action  is  the  result  of  the  secondary  stimulation  of  one 
nerve,  through  a  central  organ,  by  the  primary  stimulation 
of  some  other  nerve.  On  the  other  hand,  all  excitations 
of  the  nervous  system  which  originate  in  the  nervous 
centres  themselves  are  called  "automatic."  Doubtless 
this  term  must  often  be  used  to  conceal  our  ignorance  of 
the  real  origin  of  a  neural  process ;  doubtless  also,  many 
processes,  which  at  first  sight  appear  to  be  automatic,  are 
afterwards  discovered  to  originate  reflexly.  Notwith- 
standing this,  nervous  impulses  which  result  in  the  move- 
ments of  the  muscles,  or  in  the  inhibition  of  such  move- 
ments, apparently  originate  in  the  central  organs  under 
the  action  of  internal  stimuli.  But  such  automatic  activi- 
ties belong  distinctively  to  the  central  ganglia  of  the 
brain. 

Kinds  of  Reflex  Action.  —  Theoretically,  various  kinds  of 
reflex  nervous  action  are  supposable  in  the  nervous  system. 
Thus  two  motor  nerves  might  be  combined  through  a 
central  organ  ("  co-motor  reflexes ") ;  or  an  excitation 
arising  in  a  motor  nerve  might,  without  an  act  of  will,  be 
transferred  to  one  or  more  sensory  paths  ("reflex-sen- 
sory"). As  to  the  existence  of  "co-sensory  reflexes" — or 
cases  where  the  excitation  of  one  peripheral  sensory  nerve, 

135 


136  PHYSIOLOGICAL   PSYCHOLOGY. 

through  the  central  organ,  occasions  the  excitation  of 
another  locally  different,  peripheral,  and  sensory  nerve  — 
there  can  be  little  doubt.  The  nose,  for  example,  may  be 
made  to  tickle  by  looking  at  the  sun  ;  and  strong  rubbing 
or  squeezing  of  one  muscle  may  sometimes  occasion  pain 
in  muscles  located  far  away  on  the  surface  of  the  body. 
But  only  one  kind  of  reflex  functions  of  the  nervous  system 
seems  hitherto  to  have  been  made  available  for  purposes 
of  scientific  experiment.  These  are  the  so-called  "reflex- 
motor,"  or  "sensory-motor."  Such  terms  are  given  to  reflex 
action  when  a  motor  nerve  is  stimulated  in  a  secondary 
way,  through  a  central  organ,  by  applying  stimulus  to 
sensory  nerve-endings. 

We  must  carefully  guard  ourselves,  however,  from  the 
misconception  that  lurks  in  the  word  "reflex."  The  effect 
of  the  central  organ  is  never  that  of  simply  turning  back, 
or  reflecting,  a  nerve-commotion  from  one  path  to  another. 
On  the  contrary,  the  passage  of  a  nerve-commotion  through 
a  central  organ  profoundly  modifies  both  the  condition  of 
the  organ  and  the  character  and  distribution  of  the  nerve- 
commotion  itself. 

THE  SPINAL   CORD  AS  A  CENTRE  OF  REFLEX 
MOTOR  ACTIVITIES. 

Our  previous  survey  of  the  structure  of  the  spinal  cord 
suggests  the  truth  that  it  is  specially  adapted  to  act  as  a 
central  organ  in  the  exercise  of  a  variety  of  reflex-motor 
functions.  The  older  investigators  assumed  a  great  variety 
of  special  mechanisms,  consisting  of  distinct  systems  of 
sensory  and  motor  nerve-fibres,  with  connecting  cells,  appro- 
priated for  the  sole  purpose  of  executing  the  various  kinds 
of  reflexes.  Modern  investigation  tends  rather  toward  the 
view  that  there  are  no  special  elements  of  the  cord  appro- 
priated merely  to  reflex-motor  functions.  The  whole 
structure  of  the  organ  is  such  as  to  adapt  it  in  all  its  parts, 
for  this  as  well  as  for  other  nervous  activities. 


KEFLEX   AND   AUTOMATIC    NERVOUS    FUNCTIONS.     137 

The  Reflex-Motor  Machine.  —  The  most  convenient  piece 
of  mechanism  for  experimenting  to  discover  the  laws 
of  spinal  reflexes  is  the  so-called  u  brainless  frog."  This 
preparation  consists  of  the  spinal  cord,  still  alive,  but  sep- 
arated from  the  brain  by  section  below  the  medulla  oblon- 
gata.  If  the  flank  of  such  a  frog  be  touched,  a  slight 
twitching  of  the  muscles,  which  lie  immediately  below  the 
spot  of  the  skin  thus  stimulated,  will  result  as  a  reflex 
motion.  If  a  hind  leg  be  stretched  out  and  pinched  it  will 
respond  in  a  purposeful  way  to  withdraw  itself  from  the 
irritation.  Increasing  the  strength  of  the  stimulus  will 
elicit  reflex  motions  involving  the  fore  leg  of  the  same 
side ;  then  both  legs  of  the  other  side;  and  perhaps,  finally, 
all  the  muscles  of  the  body.  If  when  one  leg  of  a  brain- 
less frog  is  irritated  it  is  at  the  same  time  prevented  from 
movement,  the  cord  of  the  preparation  will  sometimes  use 
the  other  leg  to  accomplish  the  purpose  of  removing  the 
irritation. 

Phenomena,  similar  to  those  obtained  from  the  brainless 
frog,  may  be  obtained  from  other  brainless  animals.  A 
decapitated  salamander,  when  the  skin  of  one  of  its  sides 
is  pinched,  will  bend  that  side  into  a  concave  shape. 

It  was  for  some  time  supposed  impossible  to  obtain  simi- 
lar phenomena  from  the  spinal  cord  of  mammals.  And, 
indeed,  the  spinal  reflexes  in  the  case  of  a  mammal  whose 
cord  has  been  disconnected  from  his  brain,  are,  immedi- 
ately after  section,  comparatively  weak  and  purposeless. 
But  if  such  an  animal  be  kept  alive  for  some  time,  then 
strong,  varied,  and  purposeful  movements  will  follow 
sensory  stimulation  of  the  skin  of  the  parts  below  the 
place  of  section.  After  some  weeks  or  months,  reactions 
resembling  those  described  in  the  case  of  the  frog  begin  to 
appear.  Moreover  —  a  very  significant  fact !  —  it  is  found 
that  the  breed,  sex,  age,  and  training  of  the  animal  deter- 
mine the  character  of  these  reflex  brainless  movements. 


138  PHYSIOLOGICAL   PSYCHOLOGY. 

Strength  and  Suddenness  of  Spinal  Reflexes.  —  Continuous 
irritation  of  the  skin  of  a  brainless  animal,  if  slowly  in- 
creased, does  not  give  rise  to  reflex  movements.  But  a 
much  smaller  degree  of  stimulus,  if  suddenly  applied,  will 
call  forth  such  movements.  Repetition  of  the  shocks  with 
the  electrical  current  is  much  more  effective  than  is  the 
constant  current,  in  starting  spinal  reflexes.  And  here 
we  are  reminded  again  of  the  law  already  announced,  as 
holding  good  in  "  general  nerve-physiology  "  (see  p.  125). 
A  decapitated  frog  may  be  placed  in  water,  and  the  water 
slowly  heated  until  its  life  is  destroyed,  without  its  show- 
ing any  reflex  activity.  Even  normal  frogs  —  though  with 
much  more  difficulty  —  can  be  heated,  either  locally,  with 
one  leg  in  the  water,  or  all  over,  while  sitting  on  a  cork 
in  a  cylinder  of  water,  without  causing  motion,  if  the 
increase  of  temperature  be  gradual  enough. 

Speed  of  Spinal  Reflexes.  —  It  has  already  been  said 
(p.  132)  that  the  process  of  conduction  suffers  a  delay  while 
passing  along  the  spinal  cord.  The  time  of  "cross-con- 
duction "  in  the  cord  also  seems  to  depend  upon  the 
strength  of  the  stimulus.  By  increasing  its  strength  — 
it  has  been  calculated  —  the  time  consumed  by  the  spe- 
cifically central  processes  may  be  diminished  from  0.055  to 
0.047  of  a  second.  With  very  strong  stimulus  the  time 
occupied  by  the  central  processes  becomes  almost  too  brief 
to  detect. 

Condition  of  the  Spinal  Cord.  —  The  character  of  the 
resulting  reflex  movement  is  very  largely  determined  by 
the  condition  of  the  cord  when  the  sensory  impulses  enter 
it.  Lesion  increases  the  excitability  of  the  part  below  the 
lesion.  Some  drugs  heighten  and  some  depress  its  excit- 
ability. When  the  cord  is  poisoned  with  strychnine,  for 
example,  the  slightest  stimulation  will  cause  such  an 
explosion  -in  it,  and  such  a  diffusion  of  eiiergy  along 
unaccustomed  paths,  that  convulsive  cramping  is  occa- 


KEFLEX   AND  AUTOMATIC   NERVOUS   FUNCTIONS.    139 

sioned  over  the  entire  body.  Changes  of  temperature  also 
seem  to  affect  the  reflex-motor  activities  called  forth  by 
stimulating  the  spinal  cord. 

Effect  of  Locality.  —  The  extent  and  character  of  the 
spinal  reflexes  depend,  in  a  remarkable  way,  upon  the 
locality  to  which  the  stimulus  is  applied.  The  most 
remarkable  difference  is  perhaps  that  evoked  by  irritating 
some  spot  on  the  skin  of  the  brainless  animal,  and  then 
comparing  the  result  with  that  obtained  by  applying  the 
stimulus  directly  to  the  trunk  of  the  sensory  nerve.  A 
slight  irritation  of  the  skin  may  result  in  the  extended 
movement  of  many  muscles,  combined  in  a  purposeful 
way.  The  direct  stimulation  of  the  trunk  calls  forth 
irregular  movements  in  a  few  muscles  only.  What  par- 
ticular reflex  actions  follow  stimulation,  depends  upon  the 
particular  locality  of  the  skin  to  which  the  stimulus  is 
applied. 

Laws  of  Spinal  Reflexes.  —  The  most  general  rule  of  the 
reflex-motor  activities  of  the  spinal  cord  may  be  stated  in 
terms  like  the  following :  The  irritation  of  a  sensory  nerve 
with  a  small  degree  of  stimulus  gives  rise  to  reflex  move- 
ments which  originate  in  the  cord  on  the  same  side,  at 
about  the  same  altitude  as  that  at  which  the  sensory 
impulses  enter  the  cord;  increased  stimulus  gives  rise, 
also,  to  movements  that  arise  on  the  other  side  of  the  cord, 
at  about  the  same  altitude  ;  a  still  greater  increase,  to  those 
that  originate  on  both  sides  of  the  cord,  with  the  prefer- 
ence, however,  to  the  same  side. 

It  would  seem,  then,  that  the  nerve-commotion  which 
enters  the  cord  is  dispersed,  first,  along  the  network  of 
cells  and  fibres  near  the  point  of  entrance  on  the  same 
side ;  then,  across,  at  the  same  altitude,  to  the  other 
side ;  then,  up  and  down  on  both  sides  of  the  cord. 
Excitation,  started  anywhere  in  the  cord,  tends  to  radiate 
in  all  directions,  but  with  the  preference  for  certain  paths 


140  PHYSIOLOGICAL   PSYCHOLOGY. 

marked  out  by  the  structure  and  habits  of  the  cord. 
Hence  the  spinal  cord  has  been  called  "  the  organ  for  the 
dispersion  of  irritation." 

Alleged  Automatic  Functions  of  the  Spinal  Cord,  —  This 
organ  is  not  capable  of  "  irregular  automatism,"  —  that  is, 
of  such  spontaneous  excitation  as  takes  place  in  the  higher 
centres  of  the  brain,  on  volition.  It  does,  however,  dis- 
charge certain  functions  that  are  less  certainly  reflex  than 
those  which  have  already  been  considered.  What  is  called 
the  "tonic  action"  of  the  cord  upon  the  muscles  is  a 
marked  instance  of  such  functions.  The  fact  that  this 
action  does  not  simultaneously  contract  all  the  muscles 
connected  with  the  cord,  or  any  one  set  of  them  with  the 
same  energy  as  any  other,  throws  some  suspicion  on  its 
automatic  character.  Moreover,  we  can  often  ascribe  the 
"  tone  "  of  the  muscles  of  the  brainless  animal  to  the  action 
of  subtle  influences,  such  as.  movements  of  the  air,  etc., 
upon  the  surface  of  the  skin.  If  a  brainless  frog  be  hung 
up,  after  having  the  sciatic  plexus  cut  on  one  side,  the 
muscles  of  the  leg  on  the  other  side  have  the  better  "  tone." 
But  the  same  flaccid  condition  of  the  muscles  on  the  cut 
side  exists  when  only  the  sensory  roots  of  this  plexus  are 
cut. 

The  circulation  of  the  blood  in  a  brainless  animal  seems 
to  be  in  a  measure  dependent  upon  the  condition  of  the 
spinal  cord.  Hence  it  is  claimed  that  so-called  "  vaso- 
motor  centres "  exist  in  the  cord.  Circulation  may 
continue  with  regularity  in  a  decapitated  frog ;  but  the 
removal  of  any  considerable  part  of  the  cord  affects  it. 
This  result  appears  to  arise  through  the  loss  of  tone  thus 
occasioned  in  the  blood-vessels;  and  the  mechanisms  for 
expanding  and  contracting  these  vessels  are  apparently 
interlaced  with  those  for  contracting  the  skeletal  muscles, 
in  all  parts  of  the  cord.  Hence  the  possibility  that  part, 
at  least,  of  the  result  may  be  reflex  rather  than  automatic. 


REFLEX   AND   AUTOMATIC   NERVOUS   FUNCTIONS.    141 

Centres  in  the  Spinal  Cord.  —  The  mechanism  of  this 
central  organ  is  so  constituted  as  to  connect  the  motor 
with  the  sensory  tracts,  more  favorably  in  some  regions  than 
others.  Such  regions  are  called  "  reflex  centres  "  of  the 
spinal  cord.  A  considerable  and  indefinite  number  of  such 
centres  exist;  and  some  of  them  have  been  located.  It 
has,  indeed,  been  laid  down  as  a  general  principle  that 
"the  spinal  cord  is  the  proximate  centre,  the  proximate 
physiological  hearth  of  excitation,  for  all  the  nerves  that 
originate  from  it."  Since  the  very  influential  experiments 
of  the  German  investigator,  Goltz,  upon  the  spinal  cord  of 
dogs,  many  functions  formerly  ascribed  to  the  brain  have 
been  shown  to  have  their  proximate  centres  in  the  cord. 

The  spinal  reflex  centres  of  different  animals  differ  ac- 
cording to  their  structure  and  habits.  With  frogs,  stimu- 
lation of  any  portion  of  the  skin  induces  reflex  movements 
in  all  of  the  muscles.  With  rabbits,  however,  a  reflex 
action  of  a  hind  leg  can  be  caused  by  sensory  stimulation 
of  a  fore  leg,  only  in  case  one-third  or  more  of  the  medulla 
oblongata  is  left  attached  to  the  cord.  "  Trotting  reflexes  " 
—  that  is,  movements  of  the  diagonal  opposite  extremities 
by  stimulation  of  one  limb  —  can  be  obtained  only  in  ani- 
mals with  which  such  movement  is  natural.  According  to 
the  researches  of  Ferrier  and  Yeo,  the  stimulation  of  each 
motor  root  of  the  nerve-plexuses  of  monkeys  calls  forth 
combined  movements  involving  the  co-operation  of  nu- 
merous muscles  widely  separated  anatomically.  But  all 
the  resulting  movements  are  such  as  are  seen  associated 
together  in  the  ordinary  activity  of  the  animal. 

The  spinal  cord  of  every  animal  seems,  then,  to  be  an  em- 
bodiment of  the  specific  functions  and  of  the  habits  of  the 
species  to  which  the  animal  belongs  ;  as  well  as  of  the  indi- 
vidual peculiarities  acquired  by  the  animal  in  the  previous 
use  of  the  cord. 

Nothing  more  than  a  reference  is  necessary  to  the  vari- 


142  PHYSIOLOGICAL  PSYCHOLOGY. 

ous  centres  which  experiment  discovers  in  the  spinal  cord, 
—  such  as  the  vaso-motor,  those  for  micturition,  defecation, 
parturition,  etc. 

Excitability  of  the  Cord  as  a  Whole.  —  The  question  has 
been  much  debated  whether  the  spinal  cord  as  a  whole  is 
excitable  or  not.  Some  have  held  that  the  movements 
obtained  by  applying  a  strong  stimulus  directly  to  the  cord 
arise  only  reflexly,  —  in  so  far,  that  is,  as  the  stimulus 
involves  the  sensory  roots.  The  cord,  therefore,  is  held  to 
contain  no  motor  elements  that  are  directly  excitable 
except  the  central  paths  of  the  nerve-roots.  Others  have 
held  that,  while  the  gray  matter  is  absolutely  inexcitable 
and  the  posterior  columns  very  excitable,  the  anterior 
columns  possess  only  a  moderate  degree  of  excitability. 
The  evidence  is  therefore  conflicting.  It  is  scarcely  pos- 
sible to  be  more  precise  than  to  affirm  that  certain  longi- 
tudinal parts  of  the  cord  are  susceptible  to  direct  irrita- 
tion, —  without  saying  what,  exclusively,  these  parts  are. 

Inhibitory  Effect  of  the  Brain.  —  If  the  legs  of  a  frog  are 
allowed  to  dip  into  dilute  acid,  the  interval  between 
contact  with  the  acid  and  the  withdrawal  of  the  cord  is 
considerably  lengthened  when  the  spinal  cord  remains  undi- 
vided below  the  medulla  oblongata.  The  cord  alone  with- 
draws the  leg  quicker  than  the  cord  as  influenced  by  the 
brain.  Moreover,  the  cord  alone  can  be  depended  upon  to 
respond  with  great  regularity,  in  the  form  of  definite  reflex 
movements,  to  a  given  amount  of  irritation  applied  to  a 
particular  spot.  But  connection  with  the  brain  disturbs 
this  regularity.  The  cord  is  thus  said  to  be  inhibited  by 
the  brain.  We  cannot,  accordingly,  so  well  calculate 
what  the  cord,  when  under  the  influence  of  the  brain,  will 
do. 

We  do  not  enter  upon  the  disputed  question  whether  a 
special  inhibitory  apparatus  belongs  to  the  brain  in  its 
connection  with  the  spinal  cord.  There  are  no  sufficient 


REFLEX  AND   AUTOMATIC   NERVOUS   FUNCTIONS.    143 

grounds  for  assuming  the  existence  of  such  a  mechanism ; 
but  then,  as  Dr.  Ferrier  has  said :  "  The  nature  of  the  inhibi- 
tory mechanism  is  exceedingly  obscure."  The  important 
thing  to  notice,  however,  is  that  the  cord,  while  having  a  cer- 
tain independent  power  of  functioning  in  various  ways,  is 
controlled  by  the  higher  centres  of  the  brain.  Were  this  not 
so,  we  could  not,  on  the  one  hand,  commit  to  it  the  task  of 
doing  reflexly  so  many  things  for  us ;  and,  on  the  other 
hand,  make  it  carry  out  our  desires  by  acting,  or  refraining 
from  acting,  according  to  our  will.  In  standing,  walking, 
running,  playing  upon  musical  instruments,  writing,  using 
tools,  etc.,  the  activities  requisite  are  exceedingly  complex. 
They  involve  a  complicated  and  rapid  interchange  of  the 
following  three  processes :  (1)  spinal  reflexes ;  (2)  reflex- 
motor  impulses  that  imply  the  trained  inhibitory  and 
controlling  action  of  the  centres  of  the  brain  in  con- 
nection with  the  special  organs  of  sense ;  and  (3)  special 
and  more  definite  motor  innervations  that  are  due  to  con- 
scious acts  of  volition.  For  all  the  life  of  habit  in  its 
control  over  the  movements  of  the  trunk  and  limbs,  and 
for  the  possible  inhibition,  breaking,  or  changing  of  such 
habit,  the  functions  of  the  cord  in  their  relations  to  the 
functions  of  the  higher  parts  of  the  cerebro-spinal  axis, 
are  indispensable. 

REFLEX  AND  AUTOMATIC  FUNCTIONS  OF  THE  LOWER  BRAIN- 
CENTRES. 

On  passing  from  the  spinal  cord  into  the  brain,  the  diffi- 
culty of  determining  the  special  functions  of  the  different 
nervous  centres  becomes  greatly  increased.  The  phe- 
nomena become  much  more  complicated ;  and  the  parts  are 
less  easily  reached  for  purposes  of  observation  and  experi- 
ment. 

Methods  of  Observation  and  Argument,  —  The  methods  of 
research  into  the  functions  of  the  central  organs  of  the 


144  PHYSIOLOGICAL  PSYCHOLOGY. 

brain  are  chiefly  these  two,  —  stimulation  and  extirpation. 
Both,  of  course,  can  be  in  general  applied  only  to  the 
lower  animals.  In  the  first  method,  some  form  of  stimulus 
is  used  to  irritate  a  definite  locality  in  the  brain,  and  the 
results  of  such  irritation  are  carefully  noted.  To  use  this 
method  the  organs  must  be  exposed.  With  the  skill  and 
safeguards  of  modern  surgery  this  can  be  done  for  a  con- 
siderable portion  of  the  brain,  without  permanent  injury 
to  other  organs  or  death  of  the  animal.  Those  organs  that 
lie  deepest  cannot  be  treated  by  this  method  with  the  same 
success.  The  stimulus  of  the  electrical  current  is  by  far 
the  most  convenient  for  experiment;  but  care  must  be 
taken  to  circumscribe  the  effects  of  its  diffusion  through 
the  surrounding  substance. 

With  the  method  of  extirpation,  the  difficulties  and  the 
need  of  caution  are  even  greater.  The  "  secondary  "  effects 
of  the  lesion  of  any  part  of  the  brain  of  an  animal  are  often- 
times greater  than  those  which  can  be  justly  ascribed  to 
the  injury  of  the  organ  primarily  affected.  On  the  whole, 
then,  it  is  very  difficult  to  arrive  at  a  consistent  view  of 
the  facts.  The  phenomena  observed  are  often  confusing 
and  even  apparently  self-contradictory. 

The  argument  from  such  data  of  facts  can  scarcely  be 
expected  to  yield  a  perfect  demonstration.  Valid  objec- 
tions may  be  raised  to  the  very  nature  of  the  inferences  made 
by  many  observers.  It  is  a  doubtful  assumption,  for  ex- 
ample, that  the  activities  which  remain,  when  some  of  the 
organs  of  the  brain  of  an  animal  are  extirpated,  belong 
wholly  to  the  organs  that  remain,  while  the  activities  that 
have  disappeared  belong  wholly  to  the  organs  that  have 
disappeared.  In  such  an  exceedingly  complicated  mechan- 
ism as  the  brain,  with  its  extremely  complex  and  close 
interrelation  of  parts,  the  distinct  marking  off  of  "  organs," 
and  "  areas,"  and  "  centres,"  does  not  command  our  perfect 
confidence.  Specific  differences  belonging  to  different 


REFLEX  AND   AUTOMATIC   NEKVOUS   FUNCTIONS.    145 

kinds  of  animals,  and  individual  differences  between  the 
different  members  of  the  same  species  (in  the  case  of  the 
higher  animals),  must  certainly  be  much  more  taken  into 
account  than  they  have  heretofore  been.  It  is  difficult  to 
credit  the  inference  that  a  particular  portion  or  area  of  the 
brain's  substance  is  the  (only)  organ  for  particular  func- 
tions, so  long  as  instances  may  be  brought  forward  where 
the  function  has  been  discharged  in  the  absence,  or  after 
the  destruction,  of  such  alleged  "  organ." 

The  difficulties  of  investigation  of  this  subject  are  great- 
est in  the  case  of  man.  For  man,  of  all  the  animals,  has  the 
most  complicated  brain,  and  the  most  complex  system  of 
functions  connected  with  this  organ.  Moreover,  he  is  of 
all  animals  apparently  —  in  his  developed  and  adult  life  — 
least  dependent  for  his  higher  psychical  activities  upon  the 
condition  of  any  small  circumscribed  portions  of  the  brain. 
Nor  can  he  be  experimented  with  as  can  the  lower  animals. 
Inferences  from  them  to  him  need  to  be  guarded  with 
special  care,  so  much  does  he  differ  from  them  both  in 
brain  and  in  mind.  The  testimony  of  pathology  is,  gener- 
ally, far  from  satisfactory.  For  when  disease  destroys  the 
substance  of  his  brain,  it  does  not  nicely  limit  or  definitely 
announce  the  stage  and  spreading  of  the  lesion  it  produces. 

In  spite  of  all  difficulties,  however,  the  localization  of 
reflex  and  automatic  functions  in  the  brain  of  the  higher 
animals,  including  man,  has  made  great  progress  within 
the  last  twenty  years.  Indeed,  it  is  within  this  time  that 
the  science  of  "  cerebral  localization  "  may  be  said  to  have 
been  established.  It  is  even  at  present  worth,  for  man,  far 
more  than  it  has  cost,  whether  of  scientific  painstaking  on 
his  part,  or  of  pain-bearing  on  the  part  of  the  lower  an- 
imals. It  promises  for  the  future  a  great  extension  of  our 
knowledge  of  the  relations  of  man's  body  to  his  mind; 
and  —  what  is  even  more  important  —  the  ameliorating  or 
cure  of  some  of  the  most  distressing  of  human  ailments. 


146  PHYSIOLOGICAL  PSYCHOLOGY. 

PARTICULAR  FUNCTIONS  OF  THE  MEDULLA   OBLONGATA. 

Above  the  spinal  cord  the  medulla  is  the  organ  about 
whose  functions  we  have  the  most  precise  information.  In 
general  it  may  be  said  to  be  the  organ  of  the  "  vegetative  '? 
and  also  of  the  lowest  animal  life. 

Reflex-Motor  Functions  of  the  Medulla.  —  These  are  more 
intricate  and  of  a  higher  order  than  those  belonging  pri- 
marily to  the  spinal  cord.  They  are  particularly  such  as 
stand  related  to  the  vital  functions  of  the  heart  and  blood- 
vessels ;  to  respiration  and  its  allied  movements  in  cough- 
ing, sneezing,  etc. ;  to  muscular  movement  in  swallowing, 
vomiting,  etc. ;  and  to  the  mimetic  movements  of  laughing 
and  weeping.  Some  of  these  functions  are  purely  reflex, 
some  only  partially  so.  Thus  one  cannot  swallow  except 
through  action  of  the  medulla ;  but  the  lungs  and  heart  con- 
tinue to  move  after  the  paths  between  them  and  this  organ 
are  destroyed.  Sensory  stimulation  of  the  medulla  may 
occasion  reflex  movements  along  a  large  number  of  motor 
tracts.  Thus  irritation  of  the  throat  will  occasion  simul- 
taneously, swallowing,  coughing,  shedding  tears,  contortion 
of  the  countenance,  and  changes  of  respiration  and  heart- 
movement. 

Automatic  Functions  of  the  Medulla.  —  The  chief  auto- 
matic centres  of  this  organ  are  those  connected  with  breath- 
ing, the  movements  of  the  heart,  and  the  innervation  of  the 
blood-vessels.  The  excitation  in  these  cases  must  be  sup- 
posed to  originate  as  a  neural  process  within  the  organ ; 
and  the  stimulus  causing  it  is  doubtless  to  be  found  in  the 
changing  blood-supply.  The  medulla  seems  peculiarly  sus- 
ceptible to  the  condition  of  the  blood.  It  is  probably  due 
to  the  periodic  reoxidation  of  the  blood  by  the  rhythmic 
action  of  the  lungs  that  the  medulla  sends  out  rhythmic 
impulses  from  its  respiratory  centre  to  the  lungs. 

Centres  in  the  Medulla.  —  This  small  piece  of  nervous 


KEFLEX   AND   AUTOMATIC   NERVOUS   FUNCTIONS.     147 

matter  may  be  said  to  be  packed  full  of  important  vital 
centres.  Among  these  the  respiratory  centre  was  first 
located  by  the  French  physiologist  Flourens  in  the  V- 
shaped  apex  of  the  fourth  ventricle,  or  beak  of  the  Calamus 
scriptorius.  Since  the  smallest  injury  here  causes  complete 
cessation  of  respiration,  he  called  it  the  "  vital  knot "  (nceud 
vital).  Later  investigators  have  located  this  centre 
somewhat  higher  up.  With  it  the  various  modifications  of 
respiration  —  such  as  sighing,  sobbing,  yawning,  crying, 
laughing,  coughing,  sneezing,  hiccoughing  —  are  connected. 

A  vaso-motor  centre  exists  near  the  middle  part  of  the 
medulla.  It  is  probably  both  automatic  and  reflex.  The 
removal  of  the  parts  in  front  of  the  medulla  causes  no  per- 
ceptible influence  on  the  blood-pressure;  we  therefore 
conclude  that  this  organ  itself  contains  the  principal  vaso- 
motor  centres  of  the  brain.  Through  it  very  complex 
muscular  movements  connected  with  changes  in  the  circu- 
lation can  be  called  forth,  as  witness  the  effect  of  a  draught 
of  air.  In  the  same  organ  is  a  so-called  cardio-inhibitory 
centre ;  it  is  through  this  centre,  probably,  that  the  heart 
is  stopped  by  impulses  originating  in  the  brain,  when  severe 
pain  or  sudden  and  great  emotion  overpowers  us. 

The  centre  of  deglutition  lies  still  higher  up.  Destruction 
of  this  organ  makes  swallowing  impossible.  Centres  con- 
nected with  the  secretion  of  spittle,  sweat,  tears,  etc.,  have 
been  located  in  the  same  region,  —  namely,  the  floor  of  the 
fourth  ventricle.  But  we  need  not  enter  upon  further 
details  in  this  matter. 

Co-ordination  of  Movements  by  the  Medulla,  —  If  this  cen- 
tral organ  be  left  connected  with  the  spinal  cord,  but 
severed  from  the  organs  lying  above  it,  the  frog  thus  pre- 
pared becomes  a  more  complex  mechanism  than  is  a  simple 
spinal  cord.  Such  a  preparation  will  execute  movements 
which  the  cord  alone  cannot  execute.  It  will  not,  indeed, 
move  spontaneously ;  but  when  irritated,  by  being  placed 


148  PHYSIOLOGICAL   PSYCHOLOGY. 

in  unnatural  or  uncomfortable  positions,  it  will  behave  in 
a  highly  purposeful  way.  Laid  on  its  back  it  will  make 
efforts  —  generally  unsuccessful  —  to  turn  over.  Placed 
in  the  water  it  will  swim,  —  with  movements  less  perfect 
than  those  of  the  normal  frog,  but  much  more  complex 
than  those  possible  for  the  cord  alone. 

The  medulla  oblongata  of  mammals  seems  capable  of 
executing  very  varied  purposeful  co-ordinated  movements 
of  the  muscles.  A  young  rat,  with  its  higher  central 
organs  severed  from  the  medulla,  will  cry  when  its  toes  are 
pinched,  will  swallow,  and  perform  complex  movements  of 
the  limbs.  Infants,  born  with  the  centres  above  this 
organ  undeveloped,  perform  the  associated  movements  of 
sucking  when  put  to  the  breast.  Moreover,  injury  to  this 
organ  seems  to  have  a  marked  effect  on  the  co-ordination 
of  the  muscles.  The  most  recent  investigations  connect 
the  upper  part  of  the  medulla  with  the  gray  matter  of  the 
third  ventricle,  and  with  the  semi-circular  canals,  in  bal- 
ancing the  animal  and  otherwise  co-ordinating  its  mus- 
cular movements,  in  response  to  impressions  of  touch. 

Associations  among  the  Centres  of  the  Medulla,  —  The  dif- 
ferent small  areas  of  this  organ  are  very  curiously  related 
in  regard  to  their  physiological  functions.  Some  of  them 
are  more  excitable  than  others.  Some  of  them  can  be 
voluntarily  excited;  but  others  cannot.  Some  of  them 
are  regularly  associated  together  in  their  functions ;  some, 
seldom;  some,  never.  We  can  voluntarily  control  the 
movements  of  the  lungs,  within  certain  limits  ;  but  cannot 
,  stop,  or  quicken,  by  a  volition,  the  movements  of  the  heart. 
-We  can  at  will  make  the  medulla  execute  a  cough,  but 
not  a  sneeze.  We  can  call  the  swallowing  centre  into 
operation  without  involving  any  other  centres.  In  general, 
the  things  which  the  medulla  does  for  us,  without  taking 
account  of  the  condition  of  consciousness,  are  much  more 
important  than  the  things  we  can  make  it  do,  by  volitional 
impulses  sent  from  the  cerebral  hemispheres. 


REFLEX   AND   AUTOMATIC    NERVOUS    FUNCTIONS.    149 


BEHAVIOR    OF  THE   ANIMAL    DEPRIVED   OF   ITS  CEREBRAL 
HEMISPHERES. 

An  animal  which  possesses  all  the  nervous  substance  of 
the  brain  except  the  cerebral  hemispheres,  is  capable  of 
executing  movements  that  differ  greatly  from  those  already 
described  as  belonging  to  the  spinal  cord  and  the  medulla 
oblongata.  .  Few  of  these  movements,  indeed,  appear  per- 
fectly spontaneous  or  highly  intelligent.  ~)And  such  move- 
ments as  have  this  appearance  may  generally  be  explained 
as  resulting  from  the  complicated  mechanical  interaction  of 
the  parts  remaining,  —  cord,  medulla,  pons,  crura  cerebri, 
cerebellum,  corpora  quadrigemina  (or  optic  lobes),  and 
basal  ganglia,  —  in  response  to  a  variety  of  connected 
sensory  impulses  to  which  the  parts  are  peculiarly  sus- 
ceptible. 

The  two  animals,  by  experiment  upon  which  most  data 
for  forming  a  conclusion  respecting  these  organs  are 
derived,  are  the  frog  and  the  pigeon.  They  are  certainly 
far  enough  removed  from  man  in  their  nervous  structure 
and  mental  life.  But  of  late,  considerable  success  has 
been  obtained  in  keeping  alive  the  higher  mammals 
after  loss  of  large  portions  of  their  cerebral  hemispheres. 
By  supplementing  such  observations  with  those  of  human 
pathological  cases,  and  by  arguing  upon  general  grounds 
of  comparative  anatomy  and  physiology,  a  tolerably  clear 
view  may  be  obtained  of  the  most  general  uses  of  all  those 
parts  of  the  brain  that  lie  between  the  medulla  and  the 
cerebral  hemispheres. 

A  frog  from  which  the  cerebral  lobes  alone  have  been 
removed  will,  when  appropriately  stimulated,  move  about 
almost  as  perfectly  as  a  normal  frog.  It  can  swim  well, 
can  leap  and  crawl.  It  can  turn  over  easily  when  laid  on 
its  back,  and  can  balance  itself  on  a  tilting  board.  Sub- 
merge it  in  water,  and  it  will  rise  to  the  surface  for  air. 


150  PHYSIOLOGICAL  PSYCHOLOGY. 

It  will  avoid  objects  by  guidance  of  the  light.  On  the 
other  hand,  it  seems  stupid,  pays  no  attention  to  flies 
placed  near  it,  and  will  remain  motionless,  if  kept  from 
irritation,  for  hours. 

The  case  of  the  pigeon  from  which  the  cerebral  hemi- 
spheres have  been  removed  has  been  frequently  investi- 
gated. Certain  details  respecting  its  behavior  have, 
however,  never  been  satisfactorily  settled.  The  most 
recent  careful  and  extended  observations  describe  the 
phenomena  about  as  follows :  For  a  few  days  after  los- 
ing their  hemispheres  pigeons  execute  no  spontaneous 
movements.  Soon,  however,  the  time  spent  by  them  in 
a  slumberous  condition  becomes  shorter,  and  they  begin  to 
wander  around  the  room  without  weariness.  Their  move- 
ments are  guided  by  sight  from  the  first.  Toward  the 
end  of  the  first  week  they  will  clamber  over  a  wall  12 
centimeters  high ;  a  few  days  later  they  will  mount  in  the 
corners  of  an  enclosure  17  centimeters  high.  Their  move- 
ments seem  perfectly  regulated  by  impressions  of  touch. 
They  balance  themselves  on  the  hand  or  the  edge  of  the 
table.  Bat  noises  do  not  appear  greatly  to  influence  their 
movements. 

But  do  the  actions  of  pigeons  thus  deprived  of  their 
cerebral  hemispheres  show  spontaneity  and  striving  for  a 
goal  ?  This  question  is  difficult  to  answer  in  a  perfectly 
conclusive  way.  Such  birds  will  move  around  by  day  in 
a  very  lively  fashion,  and  sleep  fast  at  night.  Many  of 
their  movements  seem  to  have  their  origin  in  vegetative 
functions ;  but  some  of  them  also  in  complex  impressions 
of  the  special  senses.  When  dislodged  from  the  hand,  or 
from  a  stick,  by  turning  it,  they  will  aim  their  flight  toward 
a  definite  object ;  they  exhibit  a  preference  for  one  object 
rather  than  others,  as  a  place  for  alighting.  They  do  not 
appreciate  the  color  or  smell  of  food,  and  will  eat  it  when 
soaked  in  salty  and  other  infusions ;  but  even  normal 


REFLEX   AND   AUTOMATIC   NERVOUS   FUNCTIONS.    151 

pigeons  have  scarcely  any  higher  perception  of  the  differ- 
ence between  grain  and  stones  than  that  which  is  based 
on  difference  in  size  and  weight.  They  do  not  feed  them- 
selves, —  even  when  the  grain  is  put  into  the  front  part  of 
their  bills.  It  is  doubtful  whether  this  is  due  wholly  to 
lack  of  perceptive  power  or  also  to  a  lack  of  power  for 
making  the  necessary  co-ordinations. 

On  the  whole  the  conclusion  seems  warranted  that  the 
bird  which  has  lost  only  its  cerebral  hemispheres  moves  in 
a  world  of  bodies  whose  situation,  magnitude,  and  form 
determine  its  movements,  but  whose  apperceived  relations 
to  the  bird  have  ceased  to  influence  it.  It  literally  "minds " 
nothing.  It  exhibits  no  fear  of  particular  objects;  no 
recognition  and  no  preference  —  of  a  sexual  or  other  kind. 

The  phenomena  which  occur  in  the  case  of  the  higher 
mammals,  on  partial  or  total  loss  of  the  cerebral  hemi- 
spheres, tend  to  confirm  the  same  conclusion.  The  maimed 
rabbit  or  rat  will  co-ordinate  its  muscular  movements  in 
response  to  sensory  impulses  from  the  organs  of  touch, 
hearing,  and  sight.  But  the  definitely  psychical  qualities 
seem  largely  or  wholly  to  have  departed  from  the  actions 
of  the  animal.  The  case  of  the  more  intelligent  of  these 
mammals  will  be  further  considered  in  a  subsequent 
chapter. 

The  organs  of  the  brain  which  lie  between  the  medulla 
oblongata  and  the  cerebral  hemispheres  are  all  very  inti- 
mately related  in  their  functions.  To  a  certain  extent 
they  act  independently ;  within  certain  limits  they  can 
assume  each  other's  functions.  They  have  largely  the  same 
connections  with  the  peripheral  organs  of  sense  and  motion. 
In  general,  they  may  be  said  to  constitute  that  portion  of 
the  nervous  mechanism  which  serves  as  the  central  organ 
for  the  complex  co-ordination  of  impulses  of  the  special 
senses  with  the  control  of  the  motor  apparatus.  They 
mediate  a  large  part  of  that  incessant  and  complicated 


152  PHYSIOLOGICAL   PSYCHOLOGY. 

readjustment  of  the  animal's  body  which  responds  to  the 
effect  of  the  environment  on  the  peripheral  organs  of  sense. 
We  do  not  in  this  connection  consider  to  what  extent  their 
function  necessitates  or  involves  "  sensations,"  in  the  only 
correct,  psychical  meaning  of  the  word. 

PARTICULAR  FUNCTIONS  OF  THE  CEREBELLUM  AND  BASAL 

GANGLIA. 

It  is  very  difficult  to  assign  the  particular  place  which 
belongs  to  each  of  the  organs  that  lie  between  the  medulla 
oblongata  and  the  cerebral  hemispheres,  under  their  general 
function  as  already  stated. 

Functions  of  the  Cerebellum,  —  Testimony  as  to.  the  effect 
of  the  extirpation  or  lesion  of  the  cerebellum  of  mammals 
is  very  conflicting.  Almost  the  entire  length  and  breadth 
of  its  surface,  both  gray  and  white  matter,  may  be  removed 
with  little  or  no  observable  result.  On  approaching  the 
strands  connected  with  the  middle  peduncles,  disturbances 
of  motion  begin  and  increase  rapidly  in  proportion  to  the 
amount  of  substance  removed.  Many  of  these  disturb- 
ances, however,  are  only  temporary;  permanent  disturb- 
ances occur,  as  a  rule,  only  when  the  injuries  affect  the 
lower  third  of  the  organ. 

One-sided  lesions  of  the  cerebellum  seem  to  have  a  much 
greater  effect  upon  the  co-ordination  of  motion  than  that 
obtained  from  symmetrical  lesions.  The  former  —  espe- 
cially when  sudden  —  occasion,  at  least  temporarily,  pecu- 
liar rolling  movements  of  the  eyes,  suggestive  of  vertigo. 
The  entire  body  of  the  animal  also  rolls  around  its  own 
axis,  —  generally,  though  not  invariably,  toward  the  in- 
jured side.  In  all  cases  of  lesion,  the  places  of  the  union 
of  the  cerebellum  with  the  medulla  and  with  the  crura 
cerebri  seem  most  important. 

The  evidence  of  pathology  respecting  the  functions  of 
the  cerebellum  is,  in  the  case  of  man,  even  more  conflict- 


REFLEX  AND   AUTOMATIC   NERVOUS   FUNCTIONS.     153 

ing  than  the  evidence  of  experiment  with  the  lower 
animals.  Several  well-known  instances  have  occurred 
where  the  cerebellum  was  either  entirely  wanting  or  had 
become  almost  totally  destroyed  by  disease.  In  most,  if 
not  all  of  these  instances,  the  balancing  power  of  the 
patient  was  imperfect.  Some  investigators  have  regarded 
cerebellar  ataxy  as  an  almost  unfailing  result  of  the  dis- 
ease of  the  vermis  of  this  organ ;  but  others  have  pointed 
out  numerous  cases  where  this  result  did  not  follow,  even 
when  the  disease  involved  the  entire  vermis.  During 
twenty-four  years  ending  1887,  Dr.  Allen  Starr  found  160 
cases  of  cerebellar  disease  reported  in  American  medical 
literature,  in  40  of  which  symptoms  and  autopsies  were 
somewhat  carefully  described.  Of  these  40  cases  there  was 
—  headache  in  26;  insubordination  of  the  limbs  in  25; 
vertigo  in  20 ;  vomiting  in  18 ;  blindness  in  14.  The 
same  year  a  German  authority  reported  that,  of  364  cases 
of  cerebellar  disease,  260,  or  71  per  cent.,  had  headache ;  49 
per  cent.,  nausea ;  33  per  cent.,  affections  of  the  eyesight. 

It  must  be  admitted  that  the  entire  evidence  makes  it 
difficult  to  place  much  confidence  in  any  induction  respect- 
ing the  particular  functions  of  the  cerebellum  in  man. 
But  on  the  whole,  it  indicates  that  this  organ  is  concerned 
in  securing  precision  of  adjustment  and  balance  of  the  two 
sides  of  the  body,  in  response  to  impressions  of  sense 
(especially  perhaps  of  sight  and  touch  in  the  most  general 
meaning  of  the  latter  word).  In  discharging  this  office, 
the  cerebellum  seems  to  be  connected  with  the  semicircu- 
lar canals. 

It  need  scarcely  be  added  that  modern  physiology  gives 
no  support  whatever  to  the  hypothesis  of  Gall,  who  con- 
nected sexual  feeling  with  the  cerebellum.  Nor  is  there 
any  good  evidence  to  show  that  it  is  the  particular  organ 
of  any  emotion,  instinct,  or  form  of  intelligence. 

Functions   of  the   Corpora   Quadrigemina.  —  Experiments 


154  PHYSIOLOGICAL  PSYCHOLOGY. 

upon  these  organs  are  difficult  on  account  of  their  small 
size  and  deep  situation  in  the  brain.  The  evidence  from 
lesions  produced  upon  the  lower  animals  has  for  a  con- 
siderable time  tended  to  connect  the  corpora  quadrigemina 
with  sensory  impulses^  not  to  say  sensations,  of  sight. 
Extirpation  on  one  side  appears  to  cause  blindness  of  the 
opposite  eye ;  and  the  amount  of  blindness  is  different  in 
different  animals,  as  the  decussation  of  the  fibres  in  the 
optic  chiasm  is  more  or  less  complete  in  different  animals. 
Moreover,  when  the  brain  is  removed  in  front  of  these 
organs,  and  they  are  themselves  left  intact,  the  animal  can 
still  guide  and  co-ordinate  its  motions  in  response  to  visual 
impulses.  The  reason  for  all  this  is  not  quite  clear.  It 
may  be  that  destruction  of  the  nervous  substance  in  this 
region  abolishes  those  movements  of  the  muscles,  in 
response  to  the  stimulation  of  light,  which  involve  com- 
plicated co-ordinations  with  other  excitations  of  sense,  or 
with  earlier  established  experience.  We  agree  with  the 
remark  of  Eckhard,  that  much  of  the  functions  commonly 
attributed  to  these  bodies  should  be  ascribed  rather  to  the 
region  in  which  they  lie. 

Certain  disturbances  of  motion  and  impairment  of  the 
power  of  co-ordination  of  the  muscles  controlling  the  face, 
eyes,  trunk,  and  limbs,  follow  injury  or  extirpation  of  the 
corpora  quadrigemina.  But  this  effect  also  is  probably 
largely  due  to  the  irritation  and  lesion  of  the  surrounding 
nerve-tracts.  While,  then,  these  organs  are  connected 
with  the  cerebellum,  pons,  and  medulla,  in  securing  equi- 
poise and  precision  of  movement,  it  is  scarcely  safe  to 
attempt  a  more  precise  localization  of  their  motor 
functions. 

Functions  of  the  Optic  Thalami.  —  Some  special  relation 
of  the  optic  thalami  to  impressions  of  sight  is  generally 
admitted.  The  fact  that  animals  deprived  of  their  cerebral 
hemispheres  alone  are  capable  of  adjusting  their  movements, 


REFLEX   AND   AUTOMATIC   NERVOUS   FUNCTIONS.     155 

in  a  complicated  way,  to  visual  impulses,  seems  to  indi- 
cate that  the  mechanism  of  these  organs  is  associated 
with  the  corpora  quadrigemina  in  performing  this  function. 
Disturbances  of  vision,  sometimes  amounting  to  complete 
blindness,  have  been  observed  in  human  patients  as  the 
apparent  result  of  disease  of  these  organs.  Some  observ- 
ers, as  Dr.  Ferrier,  and  even  Wundt,  have  connected  the 
optic  thalami  with  the  regulation  of  the  muscles  in  response 
to  sensations  of  touch.  The  evidence  on  which  this  con- 
clusion is  based  is,  however,  very  doubtful.  And,  indeed, 
the  part  which  they  appear  to  play  in  the  reflex-motor  and 
automatic  mechanism  of  sight  may  be  rather  due  to  secon- 
dary effects  on  the  surrounding  nerve-tracts.  It  is  even 
now  not  wholly  out  of  place  to  quote  the  remark,  made 
some  years  ago  by  the  French  authority,  Vulpian,  "  We 
know  nothing  of  the  special  functions  of  the  optic  thalami." 

Functions  of  the  Striate"  Bodies.  —  The  special  motor  sig- 
nificance of  the  corpora  striata_j,s  undoubted.  As  Dr. 
Ferrier  has  maintained,  the  rule  is,  that  stimulation  or  de- 
struction of  these  organs  in  man  and  in  the  monkey  causes 
results  almost  exactly  like  those  obtained  by  the  same 
treatment  of  the  motor  centres  of  the  cerebral  hemispheres. 
Lesions  of  the  striate  bodies,  in  the  case  of  the  animals, 
are  usually  followed  by  laming  of  the  limbs  of  the  opposite 
side.  This  result  does  not,  however,  always  occur.  In 
man,  paralysis  of  the  arms  and  legs  of  the  opposite  side 
follows  disease  of  one  of  these  organs.  And  yet  a  case 
has  recently  been  reported 1  where  destruction  of  the  ante- 
rior and  inner  parts  of  the  striate  bodies  on  both  sides  was 
followed  by  no  paralysis  of  the  limbs. 

While,  then,  there  is  much  evidence  for  the  view  of 
Wundt,  who  considers  these  ganglia  to  be  organs  pre- 
eminently for  the  co-ordination  of  those  motor  impulses 
which  are  derived  from  the  cerebellum  and  the  cerebrum, 

In  Brain,  July,  1887. 


156  PHYSIOLOGICAL   PSYCHOLOGY. 

we  cannot  affirm,  without  qualification,  that  the  striate 
bodies  are  exclusively  motor  and  the  optic  thalami  exclu- 
sively sensory. 

In  1884  J.  Ott  pointed  out  that  cutting  the  corpora 
striata  is  speedily  followed  by  a  marked  rise  of  tempera- 
ture. Other  experimenters  also  have  discovered  proofs 
that  these  bodies  are  in  some  special  sense  "  fever-centres," 
cerebral  areas  in  special  connection  with  the  vaso-motor 
system. 

Gray  Matter  of  the  Third  Ventricle.  —  Important  central 
functions  appear  to  belong  to  the  nervous  substance  which 
lines  the  floor  and  walls  of  the  third  ventricle.  One  ex- 
perimenter (Bechterew)  finds  evidence,  as  he  thinks,  that 
this  substance  operates  in  connection  with  the  olivary 
bodies  for  the  co-ordination  of  motor  impulses  with  sen- 
sory impulses  of  touch,  and  with  the  semi-circular  canals  in 
response  to  sensory  impulses  of  sound.  There  seems  no 
doubt  that  the  matter  around  the  third  ventricle  is  of 
importance  in  co-ordinating  movements  necessary  to  the 
equipoise  of  the  body  through  impulses  derived  from 
changes  in  the  axial  direction  of  the  eyes. 

It  thus  appears  —  to  repeat  from  our  advanced  point  of 
view  what  has  already  been  indicated  —  that  all  the  cen- 
tral organs  lying  between  the  cerebral  hemispheres  and  the 
medulla  oUongata  are  engaged  in  the  general  function  of 
co-ordinating,  in  a  highly  complicated  way,  the  movements 
of  the  muscles  with  the  sensory  impulses  of  the  special  organs 
of  sense.  In  the  normal  condition  this  function  is  under 
the  control  of  the  hemispheres  of  the  brain.  The  separate 
organs  form  a  complex  interrelated  system,  corresponding 
to  the  complex  psychical  life  of  motion  in  response  to  sen- 
sation. In  general,  even  in  the  case  of  the  lower  animals, 
the  functions  of  these  organs,  when  bereft  of  the  cerebral 
hemispheres,  shows  a  lack  of  psychical  quality,  of  conscious, 
and  especially  of  intelligent,  feeling,  desire,  and  planning. 


REFLEX  AND   AUTOMATIC   NERVOUS   FUNCTIONS.    157 

It  is  quite  purely  "  automatic  "  (in  the  narrow  sense  of  the 
word),  —  the  reaction,  without  intelligence,  upon  internal 
and  external  stimuli  of  a  highly  complicated  physical 
mechanism. 


CHAPTER   VII. 

MECHANICAL    THEORY    OF    THE   NERVOUS   SYSTEM. 

THAT  much  of  the  human  body  exhibits  the  struct- 
ure and  movements  of  familiar  machines,  there  can  be 
no  doubt.  Its  members  support  and  act  on  each  other 
according  to  those  laws  of  the  lever,  pulley,  ball-and-socket 
joint,  etc.,  with  which  the  science  of  mechanics  has  to 
deal.  These  laws  do  not  need  special  modification  when 
applied  to  the  case  of  the  body.  Less  obvious,  but  equally 
undoubted,  is  the  machine-like  character  of  certain  muscu- 
lar and  epithelial  structures.  The  heart,  for  example,  is  a 
pump  with  chambers  and  valves ;  and  the  flow  of  the  blood 
through  the  arteries  resembles  that  of  a  fluid  pumped 
through  conduits  of  unequal  and  changeable  sizes.  The 
lungs  may  be  compared  to  a  bellows  which  alternately 
sucks  in  and  expels  the  surrounding  atmosphere.  So  also 
is  the  pull  of  the  tendons  on  the  bones  like  that  of  a  cord 
or  chain  attached  to  a  mass,  for  its  movement. 

But  the  contraction  of  the  muscular  fibre  is  a  very  dif- 
ferent affair  from  any  of  the  movements  to  which  reference 
has  thus  far  been  made.  It  is  a  vital  motion  brought 
about  in  the  molecules  of  the  muscular  substance  by  the 
stimulus  of  the  nervous  discharge  into  it.  Yet  the  living 
muscle  may  be  looked  upon  as  a  molecular  mechanism. 
[We  choose  the  word  "  mechanism "  as  preferable  to 
machine,  because  it  does  not  imply  the  action  of  one  rigid 
mass,  as  a  mass,  on  another,  under  the  known  laws  of 
mechanics.]  It  is  a  system  of  minute  particles  of  matter 
which  act  upon  each  other  at  indefinitely  small  distances. 
158 


THEORY   OF   THE   NEKVOUS   SYSTEM.  159 

When  any  motion  is  set  up  in  one  part  of  the  system,  such 
motion  is  propagated  according  to  laws  that  are  determined 
by  the  constitution  and  arrangement  of  the  particles  them- 
selves. 

The  basis  for  a  mechanical  theory  of  the  nervous  system 
has  been  laid  in  the  considerations  of  the  previous  chap- 
ters. These  considerations  have  all  hitherto  been  such  as 
dispose  us  favorably  toward  some  mechanical  theory.  In 
the  largest  meaning  of  the  word  "mechanism,"  physical 
science  knows  of  no  other  way  to  consider  any  system  of 
interacting  masses,  or  molecules,  like  those  of  the  nervous 
system.  And  yet  the  considerations  of  the  previous  chap- 
ters have  also  prepared  us  for  the  statement  that  every 
mechanical  theory  of  the  nervous  system  must  be  very 
incomplete,  and  almost  wholly  of  a  tentative  character. 
The  behavior  of  even  a  small  piece  of  nerve  attached  to  a 
muscle  (the  so-called  "  muscle-nerve  machine  ")  baffles  the 
explanations  of  all  the  students  of  physical  science.  How 
much  more,  then,  an  organism  of  the  nervous  sort,  so 
infinitely  complicated  as  the  cerebro-spinal  axis  of  man ! 

Our  survey  of  physiological  psychology  would,  however, 
be  inexcusably  incomplete,  did  we  not  set  forth  the  more 
essential  features  of  every  mechanical  theory  of  the  ner- 
vous system.  And  the  point  we  have  now  reached  seems 
the  proper  one  for  dealing  with  this  subject.. 

Chemical  Theory  of  the  Nervous  System. — Little  can  be 
added  to  what  has  already  been  said  (see  pp.  15  ff.)  con- 
cerning the  exact  chemical  processes  which  take  place  in 
the  formation  of  the  nerve-fibres  and  nerve-cells,  or  during 
their  functional  activity.  In  the  nervous  substance,  itself, 
however,  we  find  the  same  chemical  elements  which  exist 
everywhere  in  nature ;  these  are,  especially,  the  four  ele- 
ments, oxygen,  hydrogen,  nitrogen,  and  carbon.  We  have 
no  reason  to  believe  that  the  essential  laws  of  the  combi- 
nation and  dissolution  of  these  elements  are  different  in 


160  PHYSIOLOGICAL  PSYCHOLOGY. 

this  substance  from  those  known  to  have  control  elsewhere. 
The  fact  that  the  combinations  are  not  precisely  the  same 
is  to  be  traced  back  to  the  original  constitution  and  devel- 
opment of  the  substance  itself. 

Nucleated  granules  in  the  very  chemical  constituents 
which  give  conditions  to  all  the  subsequent  activity  of  the 
molecules,  are  revealed  by  microscopic  examination  of  those 
cells  from  which  the  whole  body  springs.  In  the  original 
living  germ,  with  which  the  body  begun,  and  in  all  its 
subsequent  development,  every  chemical  change  in  the 
nervous  substance  may  be  regarded  as  a  movement  of  the 
physical  molecules,  —  under  conditions  furnished  by  their 
constitution  and  previous  arrangement. 

All  the  energy  expended  in  the  movement  of  the  body 
as  a  whole,  or  of  any  of  its  larger  masses,  originates  in 
minute  molecular  changes.  These  changes  stand,  of 
course,  in  direct  relation  to  the  chemical  constitution  of 
the  tissues  in  which  they  occur.  As  we  have  already 
seen,  nervous  substance  holds  in  store  a  large  amount  of 
easily  disposable  energy.  This  energy  is  yielded  freely 
and  rapidly,  if  anything  occurs  to  start  the  process  within 
the  system  of  molecules  of  which  the  substance  is  com- 
posed. When  the  molecules  break  up  and  recombine  their 
elements  in  simpler  but  more  staple  forms,  they  render 
kinetic  a  great  amount  of  energy  which  was  formerly 
latent. 

On  the  other  hand,  the  chemical  constitution  and  envi- 
ronment of  the  nervous  substance  are  such  as  to  place 
certain  checks  upon  the  process  of  breaking  up;  and  to 
elicit  and  enhance  the  reverse  process  of  building  the  sub- 
stance up  again  into  the  more  complex  but  unstable  com- 
binations. Thus  kinetic  energy  again  becomes  stored  for 
future  use  ;  and  expenditure  is  kept  within  the  limits  of  a 
wise  and  safe  economy.  That  one  and  the  same  stimulus 
may  facilitate  both  these  procer.es  involves  a  view  of  the 


THEORY   OF   THE  NERVOUS   SYSTEM.  161 

nervous  mechanism,  under  the  general  terms  of  a  mechani- 
cal theory,  to  which  we  shall  recur  again. 

Mechanical  Theory  of  the  Structural  Forms.  —  No  devel- 
oped mechanical  theory  of  the  significance  of  the  different 
forms,  whether  of  elements  or  of  organs  of  the  nervous  sys- 
tem, is  as  yet  possible.  Our  mental  picture  of  the  nerve- 
commotions  that  pass  from  one  nervous  element  to  another 
(nerve-fibres  or  nerve-cells)  does  not  admit  of  details  of 
differentiation  dependent  upon  minute  differences  of  struc- 
ture. In  general,  however,  we  note  the  relatively  large 
size  of  the  motor  nerve-cells.  Glimpses  of  possible  pecu- 
liarities belonging  to  sensory  as  distinguished  from  motor 
layers  or  areas  of  nervous  substance,  are  beginning  to  be 
obtained  by  histological  science. 

In  general,  the  arrangement  of  the  nervous  elements 
into  a  system  answers  to  the  demands  of  a  mechanical 
theory.  The  problem  is  one  of  concatenating  the  different 
physical  systems  of  the  body,  and  of  adjusting  the  relations 
of  the  whole  to  changes  in  the  environment.  This  prob- 
lem demands  a  threefold  exercise  of  function.  The 
mechanism  answers  the  problem  with  three  sets  of  organs 
—  namely,  the  end-organs,  the  more  strictly  conducting 
organs,  and  the  central  organs.  The  end-organs  —  as,  for 
example  and  most  strikingly,  the  eye  or  ear  —  are  mechani- 
cal contrivances  for  receiving  and  modifying  some  of  the 
forms  of  movement  which  take  place  outside  .of  the  body ; 
and  then  for  applying  these  modified  forms  of  move- 
ment to  peculiarly  differentiated  nervous  cells  and  fibres. 
It  is  the  office  of  the  great  mass  of  the  eye  to  transmit 
and  refract  the  light;  of  the  greater  part  of  the  ear  to 
transmit  and  condense  the  acoustic  waves.  But  the  ner- 
vous elements  of  the  retina,  and  of  the  organ  of  Corti, 
change  these  physical  processes  into  physiological  proc- 
esses. This  change,  too,  they  effect  as  properly  constructed 
molecular  mechanisms. 


162  PHYSIOLOGICAL   PSYCHOLOGY. 

The  nerves  also  are  mechanisms,  consisting  of  minute 
particles,  whose  structure  fits  them  to  take  up  an  agitation 
started  at  any  point,  and  transmit  it  from  molecule  to 
molecule,  in  accordance  with  the  constitution  and  laws  of 
the  molecular  system  which  they  constitute. 

The  solution  of  the  problems  in  mechanism,  which  fall 
to  the  lot  of  the  central  organs,  involves  yet  more  compli- 
cated structures  and  functions.  Among  those  problems 
are  the  following :  Incoming  molecular  disturbances  must 
be  so  modified  and  distributed  as  to  occasion  other  disturb- 
ances outgoing  along  a  number  of  definite  tracts  so  that 
co-ordinated  groups  of  muscles  may  contract,  simultane- 
ously or  in  the  right  sequence,  in  a  highly  complicated 
way.  Moreover,  the  movements  that  control  respiration, 
secretion,  digestion,  and  the  circulation  of  the  blood  and 
other  fluids,  must  be  united  so  as  to  work  to  a  common  end ; 
they  must  also  be  modified  as  the  changes  in  the  environ- 
ment require.  Still  further,  all  the  natural  processes  must, 
in  the  central  organs,  be  correlated  with  the  processes  of 
the  mind.  Only  in  this  way  can  sensations  and  perceptions 
arise,  through  the  action  on  the  body  of  external  stimuli ; 
only  in  this  way  can  perceptions,  and  their  accompanying 
desires,  emotions,  and  volitions,  get  expression  in  the 
physical  realm,  and  induce  changes  in  external  things. 

This  indefinite  and  general  view  of  the  mechanical 
structure  and  functions  of  the  nervous  system  obviously 
needs  to  be  somewhat  further  expanded. 

General  Mechanical  Office  of  the  Nervous  System.  —  The 
development  of  a  rich  and  varied  life,  both  animal  and 
intellectual,  requires  a  great  variety  of  related  sensations 
and  motions.  The  sensations  are  primarily  designed  to 
give  notice  to  the  animal  of  changes  in  his  environment  to 
which  his  condition  must  be  adapted  by  changes  of  his 
bodily  parts.  Within  certain  wide  limits,  the  same  office 
is  performed  by  sensory  impulses  which  do  not  give  rise  LC 


THEORY   OF   THE   NERVOUS   SYSTEM.  163 

sensations,  —  in  the  only  true  meaning  of  that  word,  as 
psychical  states.  But  sensations,  as  primary  psychical 
states,  form  the  basis  of  intellectual  attainment  and 
development. 

The  forces  of  external  nature  continually  irritate  the 
peripheral  parts  of  an  animal's  body.  These  forces  are  the 
stimuli  of  sensory  impulses,  only  when  they  are  converted, 
within  the  tissues  of  the  body,  into  molecular  motions  of  a 
physiological  kind.  The  mechanism  of  the  nervous  system 
accomplishes  this  work  of  conversion ;  it  then  propagates 
the  molecular  disturbances  to  the  proper  central  organs, 
and  through  them  again  to  the  external  and  muscular 
tissues  of  the  body.  Thus  the  play  of  the  energies  of 
external  nature,  instead  of  being  injurious  or  destructive, 
becomes  useful  in  maintaining  the  equilibrium  on  which 
life  depends.  It  also  becomes  educative,  — not  only  of  a 
wise  use  of  the  bodily  organs,  but  also  of  the  higher  life 
of  the  mind. 

Now  it  is  plain  that  all  this  requires  a  constant  equili- 
brating of  the  interaction  of  different  and  distant  parts  of  the 
body.  How  shall  this  general  important  office  of  "  equi- 
librating" be  performed?  Only  by  a  highly  elaborate 
arrangement  of  an  indefinitely  great  number  of  very  com- 
plex molecules.  Such  a  molecular  mechanism  is  the  nervous 
system.  The  various  forms  of  physical  energy  —  such  as 
light,  heat,  sound,  chemical  change,  etc. — set  into  molecu- 
lar agitation  certain  nicely  adapted  parts  of  this  mechanism. 
This  agitation  is  propagated  from  place  to  place,  along  the 
tracks  prepared,  and  accompanied  by  other  physical  changes 
of  a  chemical,  thermic,  and  electrical  kind.  These  func- 
tions of  the  nervous  system  are  nothing  but  the  movements 
of  physical  elements,  whose  constitution  and  changes,  when 
performing  their  work,  it  is  indeed  very  difficult  to  discover, 
but  which  undoubtedly  have  a  physical  constitution  and 
which  change  their  relations  in  space  under  laws  resembling 


164  PHYSIOLOGICAL  PSYCHOLOGY. 

those  familiar  to  general  molecular  science.  But  this  is 
precisely  what  science  understands  by  a  "molecular 
mechanism." 

On  the  other  hand,  it  cannot  be  denied  that  such  a  de- 
scription as  the  foregoing  is  not  full  and  exact  enough  to 
satisfy  the  demands  of  scientific  research.  It  is  confessedly 
based  upon  conjecture  ;  it  is  full  of  gaps  and  assumptions. 
A  complete  and  satisfactory  mechanical  theory  of  the 
nervous  system  would  have  to  answer  a  number  of  ex- 
tremely difficult  special  problems,  the  very  beginning  of  an 
answer  to  which  has  scarcely,  as  yet,  been  attained. 

What,  for  example,  is  the  precise  nature  of  those  chem- 
ical changes  which  —  we  have  every  reason  to  believe  — 
go  on  in  every  nerve  when  it  is  irritated  ?  If  the  process 
of  excitement  consists  in  the  explosive  decomposition  suc- 
cessively of  the  elements  of  the  nerve,  what  checks  the 
process  of  explosion  ?  Why  is  not  all  the  energy  expended 
by  the  excited  nerve  ?  How  does  it  manage  to  repair  itself 
so  as  to  answer,  within  certain  limits,  all  the  demands  which 
it  is  possible  to  make  upon  it  ?  So,  too,  if  we  attempt  to  bring 
the  nervous  mechanism  under  the  terms  of  a  general  elec- 
trical theory,  we  find  a  number  of  difficult  and  hitherto 
unanswerable  problems  awaiting  us.  How  shall  the  phe- 
nomena of  electrotonus  in  nerves  be  explained  in  terms  of 
any  known  electrical  theory?  How  shall  we  regard  the 
so-called  "  natural  current,"  etc.  ? 

These  immense  and  perhaps,  in  some  instances,  insuper- 
able difficulties  do  not,  however,  excuse  us  from  the  obli- 
gation to  hold  firmly  by  the  proposal  to  regard  the  nervous 
system  under  the  terms  of  a  mechanical  theory.  Molec- 
ular science  in  general  —  in  all  its  different  branches  of 
heat,  electricity,  magnetism,  etc.  —  encounters  many  and 
great  difficulties.  But  it  knows  no  other  way,  in  fidelity 
to  principles  established  by  all  scientific  experience  and  by 
all  the  past  development  of  physical  science,  than  to  face 


THEORY   OF   THE   NERVOUS   SYSTEM.  165 

the  difficulties  with  successive  attempts  to  overcome  them, 
and  thus  satisfy  all  the  phenomena  in  terms  of  a  mechanical 
theory.  In  the  nervous  system  of  man,  molecular  science 
finds  its  most  complicated  and  baffling  problems.  These 
problems,  too,  it  must  continue  to  regard  in  fidelity  to  its 
most  general  established  principles. 

It  only  remains  for  us  briefly  to  sketch  several  of  the 
forms  which  have  been  taken  by  the  attempt  to  frame  a 
precise  theory  of  the  functions  of  the  nervous  mechanism. 

Wave-Theory  of  Nervous  Action,  —  That  the  molecular 
disturbances  caused  in  the  nervous  substance  by  the  action 
of  stimuli  move  from  place  to  place,  after  the  analogy  of 
waves,  is  shown  by  all  the  phenomena  with  which  so-called 
"  general  nerve-physiology "  attempts  to  deal.  In  par- 
ticular have  we  seen  (p.  130  f.)  that  the  effect  of  several 
excitations  of  a  nerve  is  compounded,  in  some  sort,  in  the 
movement  of  the  attached  muscle.  Those  excitations 
which  are  simultaneous,  or  which  follow  each  other  with 
the  right  degree  of  rapidity,  are  "summed  up"  in  the 
nerve,  like  waves  of  nerve-commotion  piled  upon  one 
another.  Besides  cases  of  "  summation,"  those  of  "inter- 
ference "  seem  also  to  exist.  Moreover,  the  effect  of  one 
excitation,  in  certain  instances,  especially  within  the  cen- 
tral organs,  appears  to  "  facilitate  "  the  subsequent  passage 
of  other  excitations  along  the  same  path. 

Elaborate  experiments  have  been  made  to  determine  the 
laws  which  control  the  "  summation,"  "  interference,"  and 
"facilitation"  of  the  waves  of  nerve-commotion  within 
the  nervous  mechanism.  Let  the  interferences  be  called 
"  positive "  when  the  currents  are  moving  in  the  same 
direction,  and  "  negative  "  when  they  are  moving  in  oppo- 
site directions.  Certain  interferences  may  also  be  noted 
which  have  a  "heightening  "  effect;  for  the  result  actually 
produced  in  the  muscle  appears  to  be  greater  than  the 
sum  of  the  two  single  effects  gained  by  the  partial  exci- 


166  PHYSIOLOGICAL  PSYCHOLOGY. 

tations  if  uncompounded.  When,  on  the  contrary,  the 
result  is  less  than  the  sum  of  the  separate  partial  excita- 
tions, the  effect  is  said  to  be  "  depressing."  When,  in  the 
third  place,  the  result  is  reduced  to  zero,  the  effect  is 
"inhibitory."  All  the  foregoing  kinds  of  result  may  be 
obtained  by  compounding  the  nerve-commotions.  But  so 
complicated  are  the  phenomena  derived  by  the  various 
forms  of  compounding  as  to  forbid  our  regarding  the 
organs  themselves  as  simple  and  substantially  homoge- 
neous structures.  The  effects  produced  by  wave-like  "in- 
terferences "  in  a  nerve  depend  upon  the  original  molecular 
constitution  of  the  nerve  excited.  Moreover,  in  general,  the 
results  of  interference  conform  to  the  same  rules  after 
decapitation  or  poisoning  as  before.  The  interferences 
that  occur  in  reflex  action  also  follow  the  same  course  as 
those  which  occur  by  direct  stimulation  of  the  motor 
nerves. 

In  brief,  —  even  in  the  case  of  the  simple  nerve-muscle 
machine,  —  it  is  the  molecular  constitution  of  the  sub- 
stance, which  acts  as  a  mechanism,  that  determines  all 
the  many  variable  elements  resulting  from  the  molecular 
disturbance  of  this  substance. 

The  phenomena  which  the  central  organs  exhibit  when 
excited  are,  of  course,  far  more  complex  and  difficult  to 
bring  under  known  laws  of  molecular  wave-like  impulses, 
than  are  the  phenomena  of  the  comparatively  simple  nerve- 
muscle  machine.  In  general,  the  motor  excitation  of  any 
extremity  of  an  animal,  from  the  brain,  "  facilitates  "  the 
subsequent  passage  of  reflex  stimulus  affecting  the  same 
extremity;  and,  conversely,  reflex  stimulation  of  any  ex- 
tremity "  facilitates "  the  passage  of  a  subsequent  motor 
excitation  from  the  proper  area  of  the  brain  to  that  ex- 
tremity. For  example,  stimulating  the  toes  of  the  fore- 
leg of  a  rabbit  produces  a  greater  reflex  movement  of  the 
same  leg,  with  the  same  amount  of  stimulus,  if  the  cerebral 


THEORY   OF  THE   NERVOUS   SYSTEM.  167 

motor-centre  for  that  leg  has  just  been  directly  stimulated. 
Different  reflex  excitations  may  also  be  made  to  "  assist " 
each  other  in  a  similar  way.  But  by  this  method  of  ex- 
periment,  also,  certain  results  of  compounding  excitations 
are  attained  which  seem  incompatible  with  any  known 
theory  of  the  summation  or  interference  of  molecular 
wave-like  disturbances. 

Strictly  speaking,  we  cannot  represent,  without  qualifi- 
cation, the  behavior  of  a  single  nerve  under  stimulation 
from  two  currents  of  electricity  acting  upon  it  in  combi- 
nation, as  though  it  were  an  affair  of  the  "  addition  "  or 
"  subtraction  "  of  their  separate  effects.  It  is  possible  that 
a  stimulation  equal  in  amount  to  a  -f  b  may  not  excite  the 
nerve,  although  one  equal  to  b  alone  will  excite  it,  in  case 
a  current  equal  to  a  has  just  previously  been  acting  in  the 
nerve.  Excitations  already  existing  in  a  nerve,  when 
further  stimulation  is  applied,  are  then  not  simply  added 
to  or  subtracted  from  the  latter.  They  rather  tend  to  pro- 
duce obscure  molecular  changes  in  the  nerve  itself,  and 
these  changes  show  themselves,  in  the  nerve,  in  a  very 
variable  and  baffling  way,  as  places  and  phases  of  exalted 
or  depressed  excitability.  Let  a  represent  the  strength  of 
current  required  to  excite  a  nerve  in  its  normal  condition. 
When  the  nerve  itself  is  in  the  condition  of  exalted  excita- 
bility, a  current  weaker  than  a  will  excite  it ;  but  when  it 
is  in  the  condition  of  depressed  excitability,  a  current 
stronger  than  a  will  not  excite  it. 

How  obscure  and  complicated  are  the  molecular  con- 
ditions connected  with  the  excitement  of  a  nerve,  is 
further  shown  by  observing  the  effect  of  cross-section 
upon  its  behavior.  For  example,  for  some  minutes  after 
cross-section,  binding  the  nerve  produces  a  large  increase 
of  its  excitability  in  the  injured  place.  This  is  true  for 
all  kinds  of  stimuli,  including  the  electrical  current  in 
both  directions.  Five  to  ten  minutes  subsequently,  how- 


168  PHYSIOLOGICAL  PSYCHOLOGY. 

ever,  the  making  of  the  current  in  the  opposite  direction 
to  the  current  induced  by  cross-section  frequently  has  a 
diminished  rather  than  an  increased  effect. 

Electrical  Theory  of  Nervous  Action.  —  A  leading  authority 
has  declared  that  the  two  most  important  principles  which 
must  enter  into  any  theory  that  undertakes  to  explain  the 
behavior  of  the  nerves  in  relation  to  electricity  are  these : 
(1)  the  principle  of  electrical  excitation,  and  (2)  the 
principle  of  the  so-called  "  current  of  action." 

We  have  already  seen  (p.  127  f .),  that  the  passage  of  an 
electrical  current  through  a  nerve  produces  a  changed 
condition  of  excitability  called  electrotonus.  It  has  also 
been  shown  that  this  condition  varies  in  different  parts 
of  the  nerve,  with  the  distance  of  each  part  from  the  elec- 
trodes, and  with  the  strength  of  the  polarizing  current. 
The  condition  is  in  general  one  of  increased  excitability 
(and  perhaps  decreased  conductivity)  around  the  cathode, 
and  of  diminished  excitability  around  the  anode.  The 
time  required  for  the  development  of  this  condition  is  not 
perceptibly  later  than  the  electrical  current  which  occa- 
sions it.  The  condition  seems  also  to  spread  itself  over 
the  nerve  with  a  speed  equal  to  that  of  the  process  of 
excitation. 

Another  important  fact  already  noted  (see  p.  130),  is  that, 
with  the  nerve  as  with  the  muscle,  the  galvanometer  shows 
the  passage  of  a  current  when  one  of  the  electrodes  is 
placed  at  its  cut  end  and  the  other  at  its  equator.  This 
so-called  "  natural  current "  is  diminished  by  stimulating 
the  nerve,  as  is  shown  by  the  return  of  the  needle  toward 
the  zero-point  ("negative  variation"). 

How  now  shall  these  two  cardinal  groups  of  facts  be  ex- 
plained in  terms  of  a  defensible  electrical  theory?  The 
question  cannot,  at  present,  be  answered  with  all  the  accu- 
racy and  detail  which  physical  science  requires.  Consider- 
able progress  has,  however,  been  made  toward  a  probable 
answer  to  several  of  the  particular  inquiries  involved. 


THEORY   OF   THE  NEKVOUS   SYSTEM.  169 

Theory  of  the  so-called  "Natural  Current."  —  Two  ways  of 
regarding  the  phenomena  referred  to  above  as  the  "  natural 
nerve-current,"  or  "  current  of  rest,"  have  been  proposed. 
An  intelligent  choice  in  favor  of  one  of  them  now  seems 
possible.  The  first  of  these  theories  (that  of  du  Bois- 
Reymond)  holds  that  a  true  natural  current  exists  in  the 
nerves,  previous  to  their  excitement  or  injury  by  cross- 
section.  This  current  is  made  obvious  by  the  deflection 
of  the  needle  of  the  attached  galvanometer.  It  is  then  to 
be  regarded  as  the  resultant  of  the  innumerable  unobserved 
currents  belonging  to  the  separate  molecules  of  the  nerve. 
To  account  for  the  latter,  an  elaborate  theory  is  proposed, 
which  regards  every  molecule  of  the  nerve  as  a  minute 
battery  with  positive  and  negative  poles.  It  is  the  pres- 
ence of  these  molecules  which  gives  rise  to  currents  in 
the  medium  that  surrounds  them. 

In  order  to  account  for  the  fact  that  .such  "  natural " 
currents  are  exceedingly  small  or  wholly  wanting,  when 
the  structure  is  uninjured,  this  theory  is  obliged  to  resort 
to  very  complicated  and  artificial  hypotheses.  Under  this 
weight  it  may  be  said  utterly  to  break  down. 

The  rival  theory  (advocated  especially  by  Hermann) 
denies  the  existence  of  any  true  "current  of  rest"  in  un- 
injured nerves.  It  regards  the  starting  of  the  current  as 
due  to  the  injury  inflicted  by  cross-section.  For,  whenever 
a  nerve  is  cut  or  any  of  its  fibres  injured,  the  molecules  at 
once  begin  to  die.  But  this  implies  chemical  and  other 
changes.  These  changes,  in  which  the  death  of  the  mole- 
cules consists,  develop  the  electrical  currents.  The  mole- 
cules, disturbed  by  the  injury,  become  negative  toward  the 
uninjured  parts. 

Instead,  then,  of  seeking  an  elaborate  special  explanation 
for  the  phenomena  of  "  negative  variation,"  we  may  hold 
that  they  are  precisely  what  we  should  expect  in  view  of 
our  knowledge  of  general  electrical  theory.  So-called 


170  PHYSIOLOGICAL  PSYCHOLOGY. 

"  negative  variation "  is  not  due  to  the  diminution  of  a 
current  previously  existing.  It  is  simply  a  manifestation 
of  the  electro-motive  forces  which  come  into  action  at  the 
moment  and  at  the  seat  of  excitation.  As  this  wave  passes 
along  the  nerve,  each  minute  portion  of  the  nerve  becomes, 
first,  negative,  and  then  positive,  toward  the  adjoining  por- 
tions. The  resultant  of  these  small  local  currents  is  an 
excess  of  those  from  the  cut  end  over  those  to  the  cut  end, 
— that  is,  the  so-called  negative  variation. 

Thus  the  phenomena  of  the  "natural  current"  and 
"  negative  variation,"  so  called,  are  all  to  be  brought 
under  the  one  general  principle.  All  excitable  protoplasm, 
when  dying  or  irritated,  becomes  negative  towards  its  own 
uninjured  and  unirritated  parts. 

Theory  of  the  Electrotonus  of  Nerves.  —  It  has  been  said 
that  any  electrical  theory  of  the  action  of  the  nervous  sub- 
stance must  be  prepared  to  explain  the  phenomena  of 
changed  excitability  produced  by  the  constant  current  in 
the  nerve.  The  point  of  starting  for  that  form  of  theory, 
which  has  most  claims  to  credence,  may  be  taken  from  a 
discovery  made  some  years  ago  by  Matteucci.  In  1863 
this  truly  great  investigator  noticed  phenomena,  similar  to 
those  of  the  nerve  in  the  electrotonic  condition,  occurring 
in  over-spun  wires  when  moistened  with  a  conducting  fluid. 
If  an  electrical  current  be  applied  to  the  moist  covering 
of  such  a  wire,  every  part  of  the  wire  will  develop  a  cur- 
rent flowing  in  the  same  direction  with  the  primary  current, 
but  with  its  strength  diminishing  as  the  distance  increases 
from  the  points  where  the  primary  current  is  applied.  No 
such  current  arises,  however,  if  the  wire  is  made  of  amal- 
gamated zinc,  and  its  covering  is  moistened  with  a  solution 
of  sulphate  of  zinc.  It  appears,  then,  that  the  changed 
electrical  condition  of  the  wire  depends  upon  the  limiting 
surfaces  of  its  metal  centre  and  its  moistened  covering 
being  polarizable.  That  is  to  say,  as  has  been  more  re- 


THEOBY  OF  THE   NERVOUS   SYSTEM.  171 

cently  maintained,1  a  conductor  consisting  of  a  centre  and 
a  conducting  covering,  with  polarizable  limiting  surfaces, 
as  soon  as  a  momentary  electrical  current  is  sent  through 
any  portion  of  it,  begins  successively  to  exhibit  a  current 
of  the  same  kind  at  every  other  place  in  it. 

Can  a  nerve  be  regarded  as  having  the  properties  of  the 
over-spun  wire,  with  its  polarizable  limiting  surfaces  ? 
Every  nerve-fibre  may  certainly  be  said  to  consist  of  a 
centre  and  a  covering  substance.  The  needed  limiting 
surfaces  may,  perhaps,  be  found  between  the  axis-cylinder 
and  the  medullary  sheath.  An  inner  polarization,  such  as 
takes  place  between  the  wire  and  its  moistened  covering, 
may  then  take  place  between  this  core  of  the  nerve  and 
one  of  its  sheaths.  The  electrotonic  current  may,  there- 
fore, be  due  to  an  escape  of  this  polarizing  current.  Such 
a  current  is  wanting  in  dead  nerves,  because  the  requisite 
inner  polarization  cannot  take  place  in  dead  nerves. 

Various  objections  have  been  brought  against  an  electri- 
cal theory  of  the  nerve  as  formed  after  the  analogy  of 
the  over-spun  polarizable  wire.  Some  of  these  objections 
are  based  upon  very  complicated  results  which  are  gained 
by  stimulating  the  nerve  under  a  variety  of  conditions, 
and  with  the  exciting  current  applied  to  different  parts  of 
the  nerve,  —  intra-polar  as  well  as  extra-polar.  To  explain 
these  results  it  seems  necessary  to  suppose  that  a  number 
of  "  secondary  action-currents "  are  evoked  by  the  stimu- 
lus; and  that  these  currents  are  superimposed  upon  one 
another,  and  upon  the  electrotonic  variations  due  to  the 
polarizing  current  —  all  in  a  bewildering  complexity  of 
combinations.  But  —  with  the  condition  of  the  Ptolemaic 
system  just  previous  to  the  discovery  of  Copernicus  in 
mind  —  we  feel  obliged  for  the  present  to  stop  and  await 
conjectures  warranted  by  further  researches. 

It  is  perfectly  obvious  that  "  the  platinum  wire,  with  its 
1  By  Hermann,  in  Pfliiger's  Archiv,  1885,  xxxv.,  p.  23  f. 


172  PHYSIOLOGICAL  PSYCHOLOGY. 

moist  sheaths,  is  no  (complete)  model  of  the  irritable 
nerve."  A  single  nerve-muscle  preparation,  taken  from 
the  leg  of  a  frog,  behaves  in  such  a  way  as  to  show  that  it 
is,  even  as  regards  its  electrical  properties,  a  much  more 
complicated  mechanism  than  is  any  such  wire.  We  must 
confess,  then,  that  we  have  no  adequate  theory  for  explain- 
ing the  behavior  of  this  comparatively  simple  nervous 
apparatus.  How  far,  then,  are  we  from  a  complete  mechani- 
cal theory  of  the  human  nervous  system  !  Any  statement 
of  an  intelligent  and  judicious  attempt  to  form  such  a 
theory  possesses,  however,  a  certain  interest  and  value. 

Mechanical  Theory  of  Wundt.  —  In  the  attempt  to  con- 
sider the  nervous  system  as  a  molecular  mechanism  we  are 
obliged  to  reason,  for  the  most  part,  deductively.  We 
cannot  successfully  investigate  directly  the  chemical  and 
physical  constitution  of  the  nervous  elements,  and  the 
changes  which  they  undergo  in  the  discharge  of  their 
functions.  By  assuming  certain  general  principles  of 
molecular  physics,  and  especially  the  law  of  the  conserva- 
tion of  energy,  we  can  speculatively  show  how  living 
beings  may  be  brought  under  the  control  of  these  princi- 
ples. This  is  the  mode  of  procedure  adopted  by  the  Ger- 
man authority,  Professor  Wundt. 

All  living  beings  take  a  noteworthy  part  in  that  process 
of  interchanging  potential  and  kinetic  (inner  and  external) 
energy,  which  goes  on  everywhere  in  nature.  In  all  ani- 
mals which  have  a  nervous  system,  it  is  this  system  which 
controls  the  process.  The  process  itself  is  a  species  of 
combustion.  The  source  of  the  peculiar  activities  of  the 
nervous  system  in  controlling  this  process  lies  in  the 
nature  of  the  chemical  combinations  found  in  its  substance. 

The  nervous  system,  regarded  as  unaffected  by  stimuli, 
may  be  theoretically  compared  to  a  fluid  in  a  condition  of 
equilibrium.  In  fact,  however,  the  nervous  system  never 
is  in  a  condition  of  perfect  equilibrium.  Not  only  is  there 


THEORY  OF  THE  NERVOUS   SYSTEM.  173 

a  ceaseless  play  of  energy  internal  to  the  system,  in  which 
the  atoms  separate  from  their  old  combinations  as  nervous 
substance  and  reunite,  in  new  combinations,  to  form  the 
same  kind  of  substance ;  but  also  a  continuous  process 
goes  on  by  which  the  molecules  of  the  nervous  substance 
are  broken  up  to  form  less  complex  but  more  stable  non- 
nervous  compounds.  The  reverse  of  this  last  process  is 
also  constantly  going  on  in  the  body ;  the  nervous  system 
is  being  nourished,  or  built  up,  by  the  more  stable  com- 
pounds of  other  substance  being  broken  up  and  their 
atoms  used  to  form  the  nervous  substance. 

Here,  then,  are  two  processes  of  change  constantly  going 
on.  One  represents  the  passing  of  the  atoms  from  the  less 
stable  to  the  more  stable  combinations,  the  destruction  of 
the  nervous  substance,  and  the  setting  free  of  stored  or 
potential  energy.  The  energy  thus  made  apparent  Wundt 
calls  "  positive."  The  other  process  represents  the  passing 
of  the  atoms  from  the  more  stable  to  the  more  highly  com- 
plex but  less  stable  combinations,  the  repair  of  the  nervous 
tissue,  the  storing  of  energy  and  the  vanishing  of  kinetic 
energy.  The  energy  stored  up,  when  the  more  stable 
combination  vanishes,  is  called  "  negative."  The  positive 
molecular  energy  of  the  nervous  system  is  recognized  as 
heat  set  free,  as  contraction  of  the  muscles,  etc. ;  its  nega- 
tive molecular  energy  exists  in  the  form  of  heat  becoming 
latent,  or  of  inhibitory  action  upon  the  course  of  the  exci- 
tation of  the  nerves,  etc. 

Wundt  would  explain  the  process  of  excitation  and  con- 
duction in  the  nerves,  in  accordance  with  the  foregoing 
theory  of  positive  and  negative  molecular  energy.  In  all 
cases,  when  a  nerve  is  excited,  two  classes  of  opposed 
effects  are  set  up  in  its  substance.  One  is  directed  toward 
the  production  of  external  energy, — such  as  secretion, 
stimulation  of  ganglion-cells,  movement  of  the  muscles, 
etc.  The  other  is  directed  toward  the  control  of  the 


174  PHYSIOLOGICAL  PSYCHOLOGY. 

energy  thus  set  free.  The  general  law  is,  that  by  the 
application  of  stimulus  both  of  these  opposed  effects  are 
augmented  in  the  nervous  substance.  That  is  to  say,  irri- 
tating the  nervous  substance  accelerates  both  the  recom- 
bination of  the  atoms  of  its  highly  complex  molecules  in 
less  complex  but  more  stable  forms ;  and  also  the  escape 
of  the  atoms  from  these  forms  and  their  return  to  the  more 
complex  and  less  stable  combinations.  The  work  which 
the  nerve  does  external  to  itself  depends  upon  the  former 
process.  It  is  a  species  of  combustion,  in  which  the  com- 
plex molecules  break  up  and  their  atoms  pass  into  more 
stable  and  simple  combinations.  It  involves,  of  course, 
the  exhaustion  of  the  nerve.  It  implies  that  the  positive 
molecular  energy  is  more  accelerated  than  the  negative,  by 
the  irritation  of  the  stimulus.  The  entire  sum  of  energy 
thus  set  free  to  do  external  work  is  distributed  in  three 
principal  directions :  in  the  continuous  excitation  of  the 
nerve ;  in  producing  heat ;  in  producing  the  reverse  pro- 
cess of  negative  molecular  energy. 

Wundt's  theory  becomes  more  complicated  when  he 
attempts  to  apply  it  to  the  central  organs  of  the  nervous 
system.  Here  the  chief  thing  of  which  account  must  be 
taken  is  the  observed  fact  that  a  greater  amount  of  stimu- 
lus is  needed  to  move  a  muscle  through  a  collection  of 
ganglion-cells.  The  nervous  substance  of  the  central 
organs  offers  a  greater  resistance  to  the  progress  of  a  nerve- 
commotion  than  is  offered  by  the  nerves.  On  the  other 
hand,  this  substance  has  stored  within  it  a  vast  amount  of 
energy ;  it  is,  therefore,  in  a  condition  to  answer  a  demand 
made  upon  it  by  developing  a  far  greater  amount  of  work. 
Wundt  finds  proofs  for  this  view  in  the  phenomena  of 
"  reflex  poisons,"  of  "  summation,"  of  "  inhibition  "  (see  p. 
165  f .) ,  etc.  He  concludes  that  when  summation  takes  place, 
the  several  sensory  excitations  have  been  conducted  in  the 
brain  to  different  sensory  regions,  and  have  then  passed 


THEORY   OF   THE  NERVOUS   SYSTEM.  175 

simultaneously  from  them  into  the  corresponding  motor 
elements  of  the  central  organ.  But  when  inhibition  takes 
place,  the  excitations  have  been  conducted  so  as  to  come 
together  and  counteract  each  other  in  the  same  sensory 
central  region. 

Excitation  of  the  central  organs,  like  irritation  of  the 
nerves,  increases  both  their  positive  and  their  negative  ner- 
vous energy.  But  the  positive  molecular  energy  of  the 
central  organs  is  but  slightly  increased  by  a  momentary  exci- 
tation. Prolonged  excitation,  however,  causes  the  positive 
condition  —  i.e.  the  condition  of  doing  work  external  to  the 
system  —  to  predominate  over  a  wide  area.  In  the  nerve, 
as  a  rule,  the  nervous  substance  is  used  up,  and  the  pro- 
cess of  restoring  it  and  storing  energy  goes  on,  compara- 
tively slowly.  An  excited  ganglion-cell  is  in  a  condition 
analogous  to  that  of  the  nerve  at  the  anode  when  the  con- 
stant current  is  passing  through  it.  In  the  cells,  as  a  rule, 
the  production  of  the  complex  molecules  in  which  energy 
is  stored  predominates. 

The  fundamental  properties  of  nervous  matter  con- 
sidered from  the  mechanical  point  of  view  are,  according 
to  Wundt,  these  two,  (1)  to  receive  external  impressions, 
in  order  by  them  to  be  determined  in  its  own  molecular 
condition;  and  (2)  to  transform  the  potential  energy  of 
the  body  into  kinetic,  partly  under  the  immediate,  and 
partly  under  the  progressive,  influence  of  these  impressions. 

Wundt  proposes  an  elaborate  and  highly  speculative 
view  of  the  molecular  constitution  and  functions  of  the 
ganglion-cells.  But  we  refrain  from  entering  upon  a  sub- 
ject so  largely  conjectural. 

In  conclusion,  we  return  to  the  general  truth  that  the 
entire  nervous  system  may  undoubtedly  be  regarded  as  a 
vastly  complicated  molecular  mechanism.  Its  chemical  con- 
stitution is  highly  complex  and  correspondingly  unstable. 
It  performs,  as  a  mechanism,  the  general  work  of  bringing 


176  PHYSIOLOGICAL  PSYCHOLOGY. 

together  into  unity  the  functions  of  the  other  systems  of 
the  body.  It  performs  this  work  under  the  laws  of  molecu- 
lar physics.  But  what  it  does  by  way  of  function  depends 
upon  what  it  is  in  respect  to  molecular  constitution.  And 
so  complicated  is  the  application  to  it  of  the  general  theory 
of  molecular  physics  that,  thus  far,  all  the  resources  of 
that  science  have  been  quite  insufficient  to  afford  detailed 
explanations. 


CHAPTER   VIII. 

SENSORY  AND   MOTOR    FUNCTIONS    OF  THE   CERE- 
BRAL HEMISPHERES. 

OEDINARY  observation  does  not  make  known  to  us  the 
great  significance  of  the  nervous  system  for  the  life  of 
conscious  sensation  and  motion.  It  is  only  accident  or  the 
dissecting-knife  which  exposes  the  peripheral  nerves  to 
our  sight.  In  the  case  of  the  central  organs,  and  espec- 
ially in  the  case  of  the  contents  of  the  skull,  there  is  little 
in  our  daily  experience  which  leads  to  the  suspicion  of 
their  significance  or  even  of  their  existence.  That  mech- 
anism of  nerve-fibres  and  nerve-cells,  on  whose  activity  all 
our  knowledge  of  things,  including  our  own  bodies,  is 
dependent,  does  not  convey  any  direct  knowledge  of  itself. 

It  is  not  so  strange,  then,  as  might  appear  at  first  sight, 
that  the  ancients,  as  a  rule,  attached  little  importance  to 
the  brain.  The  physician  Alcmseon  is,  indeed,  reported  by 
later  writers  to  have  regarded  it  as  the  meeting-place  of 
the  senses.  A  similar  view  is  ascribed  to  the  celebrated 
Hippocrates,  and  was  accepted  by  Plato.  But  Aristotle, 
the  greatest  of  all  inductive  philosophers  in  antiquity, 
although  he  was  the  son  of  a  physician,  and  was  for  his 
time  exceedingly  well  acquainted  with  the  dissection  of 
animals,  made  little  account  of  the  brain.  He  seems  to 
have  regarded  it  as  quite  unfit  to  be  the  seat  of  the 
sensus  communis,  —  a  lump  of  cold  substance  chiefly  use- 
ful as  a  source  of  fluid  for  lubricating  the  eyes ! 

Nor  can  the  great  significance  which  modern  science 
attributes  to  the  brain  be  held  to  have  its  origin  largely 

177 


178  PHYSIOLOGICAL   PSYCHOLOGY. 

in  direct  feelings  connected  with  the  exercise  of  its 
functions. 

To  be  sure,  we  localize  in  the  head  certain  phenomena 
of  consciousness  connected  closely  with  processes  of  thought. 
The  act  of  attention,  for  example,  results  in  feelings  of 
strain  in  the  muscles  of  the  eye,  or  over  the  skin  of  the 
forehead  and  its  adjacent  parts.  Sensations  of  hearing, 
smelling,  and  tasting  originate  in  the  head,  and  some- 
times seem  to  penetrate  its  interior.  After-images,  or 
spectra,  appear  with  the  eyes  closed  as  seated  in  the  upper 
front  part  of  the  face.  We  "  talk  to  ourselves  "  within  the 
head,  as  it  were.  Eager  and  concentrated  observation,  or 
concentrated  reflection,  may  develop  painful  feelings  in 
the  cerebral  region.  Men  lean  the  head  on  the  hand  in 
support  of  meditation ;  or  rub  it  vigorously  to  awaken  the 
powers  of  memory  or  reasoning.  In  this  highly  "  nervous  " 
age,  the  attention  of  multitudes  is  undoubtedly  directed 
to  the  existence  of  sensations  localized  on  the  surface  of, 
or  within,  the  skull,  which  were  scarcely  noticed  by  the 
ancients.  It  was  the  effect  of  strong  passion  and  desire  on 
the  visceral  organs  which  attracted  the  attention  of  the 
latter,  as  all  their  language  shows.  The  brain,  in  the  popu- 
lar estimate  as  a  matter  of  seemingly  direct  knowledge,  is 
a  modern  organ. 

The  phenomena  of  self-consciousness  are  confirmed  in  a 
general  way  by  observation  of  what  happens  to  others.  A 
blow  upon  the  head,  or  the  shutting  off  of  the  blood-supply 
by  pressure  at  the  neck,  disturbs  or  suspends  conscious- 
ness. Several  of  the  principal  organs  of  sense,  regarded  as 
avenues  for  sensory  impulses,  are  so  related  to  the  contents 
of  the  cranial  cavity  as  to  suggest  'that  it  may  serve  as 
their  common  place  of  meeting.  It  was  this  obvious  fact, 
naively  interpreted,  which  led  certain  ancient  anatomists, 
like  Galen  and  Herophilus,  to  locate  the  soul  in  the  brain. 

Modern  science  is,  of  course,  not  satisfied  with  the  vague 


SENSORY   AND  MOTOR   BRAIN   FUNCTIONS.  179 

results  derived  from  feeling  and  ordinary  observation  of 
others.  It  attempts  to  establish  -definitely  and  experimen- 
tally the  function  of  the  contents  of  the  cranial  cavity  in 
the  life  of  consciousness.  In  this  attempt  it  considers, 
first,  certain  general  facts  which  connect  the  entire  brain 
of  man,  and  especially  the  cerebral  hemispheres,  with  his 
psychical  life.  It  then  tries  to  assign  the  more  particular 
functions,  connected  with  the  varieties  of  this  psychical 
life,  to  particular  parts  of  the  hemispheres.  This  investi- 
gation leads  to  "  the  localization  of  cerebral  functions." 

GENERAL  SIGNIFICANCE  OF  THE  BRAIN  FOR  THE 
PSYCHICAL  LIFE. 

A  multitude  of  physical  considerations  place  beyond 
doubt  the  supreme  influence  of  the  human  brain  upon  the 
phenomena  of  consciousness. 

Consciousness  and  the  Cranial  Blood-supply.  —  The  free  cir- 
culation of  arterial  blood,  with  its  supply  of  oxygen,  is 
necessary  to  the  central  organs  for  the  proper  fulfilment  of 
their  functions.  It  has  been  calculated  that,  while  the 
weight  of  the  entire  encephalon  is  about  one  forty-fifth  of 
the  body,  the  supply  of  blood  used  up  in  the  encephalon  is 
about  one-eighth  or  one-ninth  of  that  required  by  the 
whole  body.  The  presence  of  impurities  in  the  blood, 
derived  from  drugs  or  otherwise,  quickly  and  profoundly 
makes  itself  felt  in  modifying  the  phenomena  of  con- 
sciousness. The  quickening  of  the  circulation  by  alcohol 
or  quinine  is  productive  of  an  increased  speed  of  the  train 
of  thought  and  imagination. 

•  Consciousness  and  the  Temperature  of  the  Brain. — It  has 
been  known  for  some  time  that  a  rise  and  fall  of  tempera- 
ture in  the  substance  of  the  brain  is  connected  with  changes 
of  the  psychical  states.  Experiments  upon  the  lower  ani- 
mals lead  one  observer  to  conclude  that,  in  the  case  of  any 
animal  which  enjoys  integrity  of  the  nervous  centres,  all 


180  PHYSIOLOGICAL  PSYCHOLOGY. 

the  sensory  impressions  which  arrive  at  the  hemispheres 
produce  a  rise  of  temperature  by  their  very  transmission. 
But,  furthermore,  psychical  activity,  independently  of  the 
sensory  impressions,  develops  a  certain  degree  of  heat  in 
addition  to  that  developed  by  the  impressions  themselves. 

More  recent  experiments  seem  to  show  that  strong  im- 
pressions do  not,  as  a  rule,  result  in  a  simple  rise  of  tem- 
perature in  the  cerebral  areas,  but  rather  in  an  alternation  of 
rising  and  falling.  This  alternation  occurs  over  the  entire 
area  of  the  hemispheres,  but  with  different  speed  and 
degrees  of  augmentation  in  the  different  local  areas.  The 
elevation  is  greatest  in  the  occipital  protuberance ;  and  it  is 
greater  and  more  rapid  for  emotional  disturbance  than  for 
sensation  or  intellectual  work.  A  variation,  but  of  a  con- 
siderably less  degree,  takes  place  in  the  temperature  of 
the  brain-substance  even  in  states  of  cerebral  repose. 

The  conclusion  seems  warranted  that  these  changes  of 
cerebral  temperature  are  not  due  simply  to  changes  in  the 
arterial  circulation.  They  appear  independent  of  the 
rhythm  of  respiration,  but  dependent  on  the  rhythm  of 
metabolic  activity.  They  show  —  that  is  —  that  work  is 
beina  done  in  the  nervous  substance  in  connection  with  the 

c7 

increased  psychical  activity. 

Consciousness  and  the  Waste  of  Brain-substance.  —  An  in- 
crease in  the  gross  waste  of  tissue  can  be  shown  to  be  the 
accompaniment  and  physical  correlate  of  mental  work. 
This  waste  is  indicative  of  brain-work.  It  shows  that 
potential  energy  of  the  nervous  substance  has  become 
kinetic.  The  quantity  of  sulphates  and  phosphates  excreted, 
in  comparison  with  the  quantity  carefully  estimated  as 
entering  into  the  diet,  is  noticeably  increased  by  increasing 
the  mental  work.  To  yield  these  sulphates  and  phosphates, 
the  highly  complex  compounds  of  the  phosphorized  con- 
stituents of  the  brain  have  been  disorganized. 

Size  of  Brain  in  Different  Animals.  —  A  comparison  of  the 


SENSORY   AND  MOTOR   BRAIN   FUNCTIONS. 


181 


brains  of  different  animals  shows  a  certain  general  agree- 
ment between  their  size  and  structure  and  the  mental 
development  of  the  same  animals.  A  rough  relation 
between  the  size  of  an  animal's  brain,  relative  to  the  weight 
of  his  entire  body,  and  the  animal's  place  in  the  scale  of 
general  intelligence,  may  then  be  claimed.  The  following 
table  —  compiled  by  Exner  on  the  basis  of  the  works  of 
Carus  and  J.  Miiller  —  exhibits  this  relation :  — 


Land  Tortoise    . 

.     .     1  :    2,240 

Eagle    , 

...     1    160 

Shad               .     . 

.     .     1  •    1,837 

...     1    104 

Tadpole          .    . 

1  •       720 

Rat   .... 

...     1      82 

Elephant 

1  •       500 

Gibbon      .     .     . 

...     1     48 

Salamander    . 

.     .     1  :      380 

...     1     39 

Sheet)    . 

1:       351 

Sai-Aue 

1     25 

Fault  may,  indeed,  be  found  with  the  estimates  of  this 
table;  and,  even  if  they  are  accepted,  they  show  several 
marked  exceptions  to  the  rule  they  are  intended  to  estab- 
lish. For  example,  no  one  would  think  of  placing  the 
elephant,  in  intelligence,  behind  the  salamander  and  the 
sheep.  The  rule  itself  holds  only  in  a  loose  and  indefinite 
way. 

Growth  of  the  Brain.  —  The  brain  grows  with  great 
rapidity  for  the  first  few  years  of  the  infant's  life.  At  birth 
its  weight,  as  compared  with  the  rest  of  the  body,  is,  in  the 
male  about  1  to  5.85,  in  the  female  about  1  to  6.50.  The 
increase  in  the  weight  of  the  rest  of  the  body  is  relatively 
so  much  greater  that  by  the  end  of  the  second  year,  the 
brain  is  about  1 : 14  of  the  body's  weight ;  by  the  end  of  the 
third  year  1 : 18.  It  increases  in  absolute  weight  until 
well  on  into  middle  life ;  but  after  middle  life  it  diminishes 
at  about  the  average  rate  of  1  oz.  in  ten  years.  It  is  only 
in  a  general  and  indefinite  way  that  we  can  claim  that  the 
growth  of  the  brain  in  size  corresponds  with  the  develop- 
ment of  the  psychical  life. 


182  PHYSIOLOGICAL   PSYCHOLOGY. 

Weight  of  the  Brains  of  Individual  Men,  —  The  average 
weight  of  the  brain  of  the  adult  European  is,  for  the  male, 
from  46  to  52  oz. ;  for  the  female,  42  to  46  oz.  Many 
human  brains  rise  above  the  upper  average  ranges,  and 
some  fall  below  the  lower  average  ranges,  without  marked 
mental  peculiarities  being  connected  with  these  variations. 
Numerous  instances  of  large  excess  of  the  average  weight 
of  brain  on  the  part  of  men  of  unusual  intelligence  have 
been  recorded.  For  example,  the  brain  of  Byron  was 
scarcely  under  79  oz. ;  Cromwell,  78.8  oz. ;  Cuvier,  64.5  oz. ; 
Webster,  53.5  oz.  On  the  other  hand,  persons  of  unusual 
intelligence  have  occasionally  been  found  to  have  brains 
of  size  below  the  lower  average  just  mentioned.  And 
numerous  men  with  big  heads  and  no  corresponding 
growth  of  mental  capacity  are  to  be  noted  by  any  observer. 

The  brains  of  the  insane  are  not,  on  the  average,  below 
those  of  the  sane  in  weight.  Idiots,  on  the  contrary,  as  a 
rule,  have  brains  far  below  the  average  weight ;  and,  con- 
versely, a  brain  of  only  30  oz.,  or  under,  in  an  adult,  indi- 
cates decided  lack  of  mental  capacity,  if  not  complete 
idiocy.  Most  of  such  unfortunates  are  cases  of  arrested 
cerebral  and,  therefore,  mental  development.  It  may  be 
said,  then,  tHat  a  certain  size  or  development  of  brain- 
mass  is  necessary  to  average  intelligence;  and  that  an 
unusual  but  healthy  development  of  the  brain's  size  is 
favorable,  but  not  necessary,  to  unusual  mental  activity. 

Brains  of  Different  Races.  —  Many  data  have  been  gath- 
ered to  show  that  the  average  weight  of  the  brains  of  the 
different  races  is  indicative  of  their  place  in  the  scale  of 
human  intelligence.  Most  of  these  data  are  lacking  in  the 
requisite  scientific  exactness.  The  calculations  have  been 
made  for  the  most  part  from  the  size  of  the  cranial  cavity 
as  ascertained  by  measuring  a  large  number  of  skulls.  In 
this  way  it  is  inferred  that  the  average  weight  of  brain  in 
the  African,  Australian,  and  Oceanic  races  falls  from  1  oz. 


SENSORY   AND   MOTOR   BRAIN  FUNCTIONS.  183 

to  4  oz.  below  that  of  the  more  highly  civilized  European. 
The  weight  of  brain  among  the  Chinese,  however,  has  been 
calculated  to  be  about  that  of  the  Caucasian  race  in 
Europe.  The  low  weight  of  the  brain  of  the  Hindus  is  a 
function  of  their  smaller  bulk  of  body.  Among  savage 
races  there  seems  to  be  a  great  lack  of  cases  rising  up  to 
or  above  the  higher  ranges  of  the  weight  of  the  brain  as 
found  in  European  races.  On  this  evidence,  also,  our  con- 
clusions must  remain  only  general  and  tentative. 

Relative  Development  of  the  Hemispheres  in  Man.  —  On 
comparing  the  brains  of  different  animals  the  conviction 
becomes  irresistible  that  the  development  of  the  expanded 
and  convoluted  cerebral  hemispheres  forms  a  certain  meas- 
ure of  the  quantity  and  quality  of  the  animal^s  psychical 
life.  This  development,  in  size,  number?  and  depth7  of  the 
cerebral  convolutions,  is  the  most  distinctive  feature  of 


the  human  brain.  TrTfishes,  generally,  both  cerebrum  and 
cerebellum  are  small ;  but  there  is  relatively  an  enormous 
development  of  the  ganglia  connected  with  the  organs  of 
sense.  In  amphibia  the  cerebral  hemispheres  are  relatively 
enlarged ;  in  reptiles  they  are  pushed  still  farther  back- 
ward ;  while  in  birds  the  vesicles  of  the  mid-brain  are  par- 
tially hidden  by  the  development  of  the  hemispheres.  In 
the  lower  mammals  this  process  of  development  is  con- 
tinued; but  it  is  only  in  the  higher  mammals  that  the 
occipital  lobe  enlarges  backward  so  as  to  cover  mid-brain, 
cerebellum,  and  medulla  oblongata  ;  and  that  the  fore-brain 
so  enlarges  and  pushes  forward-  as  to  constitute  a  true 
forehead. 

Moreover,  the  forms  of  brain  found  permanently  in  the 
lower  animals  are  extremely  similar  to  those  shown  in  suc- 
I cession  by  the  development  of  the  embryo  of  the  higher 
'mammals,  and  especially  of  man.  This  higher  evolution 
of  the  brain-mantle,  as  it  appears  in  man,  is  not  attained 
without  many  breaks  in  the  animal  series.  But  through 


184  PHYSIOLOGICAL  PSYCHOLOGY. 

the  process  of  its  evolution  the  position  and  structure  of 
the  ganglia  of  the  trunk  remain  in  general  the  same, 
though  decreasing  in  relative  importance  with  the  increase 
in  the  size  of  the  mantle.  Thus  does  comparative  anat- 
omy display  the  supreme  significance  for  the  psychical  life 
of  the  cerebral  hemispheres. 

We  should  not  be  true  to  all  the  facts,  however,  if  we 
did  not  admit  that,  in  each  great  group  of  animals,  varia- 
tions occur  in  the  degree  of  cerebral  convolution,  such 
that  it  cannot  be  said  accurately  to  measure  every  ascend- 
ing degree  of  intelligence.  The  ruminants,  for  example, 
although  rather  dull,  have  numerous  and  deep  convolu- 

f  tions.     The  marmoset  shows  a  relatively  smooth  and  non- 

S  convoluted  surface  when  compared  with  other  monkeys  no 

I  more  intelligent. 

(  Individual  Differences  of  the  Cerebral  Convolutions.  —  The 
attempt  has  been  made  to  show  that  the  brains  of  less 
highly  intellectual  races,  or  individuals,  among  men  are 
relatively  poor  in  cerebral  convolutions.  The  attempt 
indicates  perhaps  a  probable  truth ;  but  it  has  not  as  yet 
succeeded  in  giving  us  a  scientific  certainty.  .  The  brains 
of  idiots  (or  cases  of  arrested  development)  are,  no  doubt, 
often  poor  in  convolutions.  We  have  already  seen  that 
an  almost  infinite  variety  exists  in  the  minutise  of  .the 
arrangement  of  the  gyri  and  sulci  of  the  human  brain. 
But  marked  anomalies  in  the  shape  of  the  head,  and  in  the 
cerebral  convolutions  —  especially  upon  the  left  hemi- 
sphere —  are  said  to  be  more  frequent  among  the  mentally 
disordered. 

Into  other  more  elaborate  attempts  to  fix  standards  for 
a  scale  of  brain  development  that  shall  measure  psychical 
activity  and  development,  we  do  not  think  it  wise  to  enter. 


SENSORY   AND   MOTOR   BRAIN  FUNCTIONS.  185 


SPECIAL   SIGNIFICANCE  OF   THE    CEREBRAL   HEMISPHERES 

IN  MAN. 

The  facts  and  conclusions  to  which  reference  has  just 
been  made  show  that  the  general  significance  of  the  brain 
for  the  psychical  life  of  man,  in  common  with  all  the  ani- 
mals, cannot  be  doubted.  They  also  indicate  that,  in 
man's  case,  the  cerebral  hemispheres  have  a  special  sig- 
nificance. The  evidence  of  comparative  anatomy  and  of 
general  physiology  points  to  that  convoluted  rind  of  gray 
matter,  which  is  the  mantle  of  the  human  brain,  as  the 
physical  crown  of  man,  in  comparison  with  all  the  other 
animals ;  as  the  physical  basis,  in  a  special  way,  of  his 
superior  psychical  life.  This  indication  is  amply  confirmed 
by  other  facts  of  physiology,  especially  of  the  experimental 
kind. 

The  simple  spinal  cord  of  a  frog,  acting  as  a  molecular 
mechanism,  will  perform  a  few  wonderful  feats  (see  p.  137). 
Joined  with  the  medulla  oblongata,  optic  lobes,  and  other 
lower  parts  of  the  brain,  it  will  show  largely  increased 
signs  of  a  complex  psychical  life.  But  there  is  great 
doubt  as  to  how  we  are  to  interpret  these  signs ;  whether, 
indeed,  they  are  to  be  understood  as  signs  of  a  psychical 
life  at  all.  The  purposeful  movements  of  the  cord  of  a 
decapitated  frog  or  salamander  have  led  some  physiologists 
to  argue  that  consciousness  must  have  its  seat  in  the  cord 
of  these  animals.  Plainly  here,  however,  the  argument  is 
scarcely  stronger  than  that  which  could  be  made  to  show 
that  a  conscious  life  has  its  seat  in  the  molecules  of  the 
climbing  plant,  or  of  those  living  corpuscles  which  float  in 
the  blood,  or  of  the  cilia  that  move  in  the  intestines. 

A  large  portion  of  the  purposeful  activity  of  the  human 
body  is  not  definitely  correlated  with  any  conscious  mental 
activity;  for  example,  breathing,  swallowing,  winking, 
changing  the  posture  of  the  body  in  sleep  or  in  states  of 


186  PHYSIOLOGICAL  PSYCHOLOGY. 

profound  meditation,  and  even  the  highly  complex  opera- 
tions involved  in  walking,  singing,  playing  on  musical 
instruments,  or  handling  tools.  In  these  and  similar  cases, 
the  intricate  purposeful  play  of  the  physical  mechanism  is 
by  no  means  necessarily  connected  with  a  corresponding 
series  of  conscious  sensations  and  volitions. 

In  proportion  as  the  hemispheres  of  an  animal's  brain 
become  relatively  developed,  not  only  their  absolute  but 
also  their  relative  significance  is  increased.  Their  in- 
fluence upon  the  movements  of  the  animal  is  greater,  the 
higher  it  stands  in  the  scale  of  cerebral  development  and  of 
intelligence.  A  frog  or  a  pigeon,  deprived  of  its  hemi- 
spheres, can  do  what  it  is  quite  impossible  for  a  dog  or  an 
ape  to  do  in  similar  condition.  Yet  the  most  marked  result 
of  the  loss  of  these  parts  of  an  animal's  brain  is  the  sudden 
and  great  departure  of  intelligence,  of  truly  psychical  or 
"mind"  quality,  from  its  life.  This  result  is,  moreover, 
the  more  marked  the  higher  the  animal  stands  in  the  scale 
of  intelligence,  whether  as  an  individual  among  its  own 
species  or  as  a  species  among  other  kinds  of  animals.  The 
more  mind  an  animal  has  to  lose,  the  more  it  actually  seems 
to  lose,  when  its  cerebral  hemispheres  are  destroyed. 

On  these  grounds  and  others  which  have  previously  been 
considered  (see  Chapter  VI.),  we  are  inclined  to  hold  that 
the  functions  connected  with  man's  conscious  psychical  life 
are  limited,  almost  wholly  if  not  exclusively,  to  the  cere- 
bral hemispheres.  Only  in  them  is  the  physical  basis  laid, 
so  to  speak,  for  the  life  of  conscious  sensation  and  volition. 
Unless  changes  in  the  peripheral  parts  of  the  nervous  sys- 
tem, and  even  in  the  lower  portions  of  the  brain,  find 
expression  in  changes  within  the  cerebral  cortex,  no  effect 
in  consciousness  results.  Conversely,  all  motor  changes 
produced  by  changes  in  states  of  consciousness  reach  the 
lower  portions  of  the  cerebro-spinal  axis,  and  the  peripheral 
parts  of  the  nervous  system,  through  effects  first  realized 


SENSORY  AND   MOTOR  BRAIN  FUNCTIONS.  187 

in  the  cerebral  cortex.  The  physical  basis  of  human 
consciousness  is  certainly  pre-eminently,  and  —  we  believe 
—  exclusively,  the  convoluted  cortex  of  the  cerebrum. 

But  the  cerebral  cortex  is  an  exceedingly  complex  organ ; 
the  rather  is  it  a  system  of  complex  organs.  It  is  not  a 
homogeneous  mass.  Its  different  areas  are  not  homogene- 
ously constructed  ;  they  have  a  variety  of  connections  and 
relations  to  the  incoming  sensory  tracts  and  to  the  out- 
going motor  tracts.  The  question  therefore  arises :  Have 
the  different  members  of  this  complex  system  of  organs 
different  relations  to  definite  motor  activities  in  the  periph- 
eral regions,  and  to  the  various  phenomena  of  conscious 
mental  life  ?  In  other  words :  Have  the  different  areas  of 
the  cerebral  hemispheres  all  the  same  office  and  value  in 
relation  to  the  life  of  sensation  and  volition  ?  This  is  the 
question  of  "  the  localization  of  cerebral  function." 

History  of  Discoveries  in  Cerebral  Localization.  —  Notwith- 
standing the  strong  presumption  in  favor  of  a  division  of 
function  among  the  areas  of  the  cerebral  cortex,  the 
experimental  science  of  cerebral  localization  dates  back 
only  twenty  years.  After  the  doctrines  of  the  older  school 
of  phrenologists  (Gall,  Spurzheim,  etc.)  had  fallen  into 
disfavor,  the  great  experimental  physiologists  pronounced 
against  the  localization  of  cerebral  function.  The  French 
authorities,  Longet  and  Flourens.,  for  example,  declared 
that  they  had  irritated  the  cortical  substance  with  a  variety 
of  stimuli  applied  to  various  localities,  and  had  extirpated 
portions  of  it  selected  from  different  places,  without  obtain- 
ing any  marked  results  upon  the  muscular  movements. 
Meynert,  indeed,  put  forth  the  opinion  that  the  anatomical 
connections  show  the  anterior  portion  of  the  cerebrum  to 
be  used  for  motor,  and  the  posterior  for  sensory  functions. 
Broca  held  to  a  special  connection  between  a  convolution 
of  the  frontal  lobe  and  the  use  of  articulate  language. 
And  in  1864  Dr.  Hughlings  Jackson  suggested  that  certain 


188  PHYSIOLOGICAL  PSYCHOLOGY. 

convolutions  superintend  those  delicate  movements  of  the 
hands  which  are  under  the  control  of  the  mind. 

It  was  not  until  1870,  however,  that  the  doctrine  of  cere- 
bral localization  began  to  be  placed  upon  a  firm  experimen- 
tal basis.  E.  Hitzig  had  noticed  that  certain  movements 
of  the  eyes  and  of  other  muscles  followed  application  of 
the  faradic  current  to  the  head  of  his  patients.  In  com- 
pany with  G.  Fritsch  he  begun  to  experiment  by  applying 
electricity  to  minute  areas  of  the  cerebral  cortex  of  dogs, 
and  watching  the  results.  The  notable  fact  was  thus  dis- 
covered that  some  areas  respond  to  stimulation  by  co- 
ordinated contractions  of  the  muscles  of  the  opposite  half 
of  the  body,  while  others  do  not ;  and  that  the  motor  parts 
lie  in  general  to  the  front,  the  non-motor  to  the  rear,  of  the 
convexity  of  the  cortex.  In  their  first  announcement  they 
indicated  five  so-called  "  motor  centres." 

Since  the  "  epoch-making  discovery "  of  Fritsch  and 
Hitzig,  many  diligent  and  skilful  investigators  have  been 
constantly  at  work;  and  the  results,  not  only  in  their 
scientific  but  also  in  their  practical  bearings,  —  as  says 
a  recent  writer,  —  "  with  the  achievements  of  antiseptic 
surgery,  constitute  the  grandest  triumphs  that  adorn  the 
history  of  the  noble  science  and  art  of  medicine." 

Kinds  of  Evidence  for  Cerebral  Localization.  —  Three  chief 
lines  of  evidence,  leading  from  three  great  groups  of  facts, 
must  be  considered.  These  are  experimentation,  pathology, 
and  comparative  anatomy.  Each  of  these  has  its  peculiar 
advantages  and  peculiar  value ;  each  has  also  its  peculiar 
difficulties  and  dangers.  The  physical  and  chemical  pro- 
cesses of  the  cerebral  substance  are  exceedingly  difficult 
of  determination.  Its  nervous  tracts  can  be  only  slowly 
marked  out,  and  that  at  cost  of  immense  and  painstaking 
labors.  Its  parts  are  so  situated  as  to  be  removed  from 
easy  observation  or  experiment.  Disease  begins  and  pro- 
gresses here  unnoticed,  or  is  only  indicated  by  symptoms 


SENSORY   AND   MOTOR   BRAIN  FUNCTIONS.  189 

which  require  the  analysis  of  an  expert.  Argument  from 
the  lower  animals  to  man  can  be  only  cautiously  applied, 
for  the  likeness  of  the  physical  structures  of  the  two  is  far 
from  perfect;  and  as  to  the  mental  life  of  the  other  ani- 
mals, we  are,  at  the  best,  much  in  the  dark.  It  is,  then, 
only  by  the  most  persistent,  candid,  and  cautious  use  of 
all  three  of  the  available  kinds  of  evidence  that  a  conclu- 
sion can  be  reached. 

Evidence  from  Stimulation.  —  In  the  localization  of  cerebral 
function  two  kinds  of  experimentation  may  be  employed. 
These  are  stimulation  and  extirpation.  The  immediate 
object  of  experiment  by  stimulation  is,  of  course,  to  dis- 
cover what  groups  of  muscles  can  be  contracted  by  apply- 
ing irritation  to  definite  areas  of  the  cortex.  It  is  assumed, 
then,  that  such  areas  are,  either  directly  or  indirectly,  con- 
nected in  some  special  way  with  the  contracting  groups 
of  muscles.  The  most  efficient  and  manageable  stimulus 
is  the  electrical  current,  but  mechanical  and  chemical 
irritation  may  be  employed  in  certain  cases. 

The  fact  that  the  same  intensity  of  the  electrical  current, 
which  will  call  into  movement  definite  groups  of  muscles, 
when  applied  to  certain  more  or  less  extended  areas  of  the 
cerebral  cortex  of  man  and  of  the  other  higher  animals, 
will  not  excite  the  same  movements  if  applied  only  a  frac- 
tion of  an  inch  distant  from  these  areas,  is  now  established 
beyond  doubt.  The  interpretation  of  this  fact,  and  the 
right  to  speak  of  these  areas  as  "  motor  "  areas,  have,  how- 
ever, been  disputed.  It  was  claimed,  immediately  after 
the  experiments  of  1870,  that  the  effects  of  the  stimulus 
were  due  to  extra-polar  conduction  of  the  electricity  in  the 
substance  of  the  brain.  This  organ,  it  was  said,  would 
diffuse  the  electricity  like  any  other  practically  homoge- 
neous substance.  It  was,  moreover,  soon  found  that,  if  a 
motor  area  be  separated  from  the  underlying  substance  by 
a  circular  cut,  it  is  excitable  with  only  a  small  increase  in 


190  PHYSIOLOGICAL   PSYCHOLOGY. 

the  strength  of  the  stimulus.  Or  if  the  gray  surface  be 
wholly  removed,  and  the  stimulus  applied  to  the  blood 
in  the  cavity,  the  customary  result  follows.  From  these 
and  other  facts  it  has  been  argued  that  these  areas  are  not 
true  cortical  "  motor  centres." 

In  answer  to  objections  like  the  foregoing  the  following, 
among  other  similar  arguments,  are  urged.  When  the 
animal  is  deeply  etherized,  the  excitability  of  the  cortical 
regions  is  wholly  or  partly  lost.  This  could  scarcely  hap- 
pen if  the  substance  of  these  regions  acted  only  as  a  homo- 
geneous conducting  medium  for  the  electrical  current.  It 
is  also  found  by  most  observers  that  a  stronger  stimulus  is 
necessary  to  move  the  muscles  from  these  centres,  after 
the  gray  substance  of  the  surface  has  been  removed.  The 
electrical  current  seems  also  to  be  retarded  in  passing 
through  this  superficial  matter;  it  is  a  fair  assumption, 
then,  that  the  interval  is  spent  in  evolving  the  particular 
nervous  function  which  belongs  to  this  matter.  Indeed, 
that  the  evidence  from  stimulation  connects  certain  por- 
tions of  the  gray  surface  of  the  brain  with  the  movements 
of  certain  groups  of  muscles,  in  a  peculiar  way,  is  now 
scarcely  to  be  denied  by  any  one  acquainted  with  the 
nature  and  extent  of  the  phenomena. 

Evidence  from  Extirpation.  —  It  is  natural  to  argue  that 
those  areas  of  the  cerebral  cortex,  whose  loss  is  followed  by 
the  loss  or  disturbance  of  motion  in  definite  groups  of  mus- 
cles, or  by  the  loss  or  disturbance  of  any  class  of  sensory 
impressions,  are  functionally  related  in  some  peculiar  way 
to  such  muscles  or  organs  of  "sense.  The  argument,  how- 
ever, needs  caution  in  application.  For  in  the  first  place,  it 
is  impossible  at  each  stage  of  the  experiment  to  know  what 
is  the  precise  condition  of  the  brain.  Local  and  extensive 
inflammations,  secondary  lesions  and  degenerations  of  the 
nerve-tracts,  cannot  easily  be  followed  by  the  experimenter 
in  detail.  It  is  generally  found  that  the  effects  of  extir- 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS.  191 

pating  any  so-called  "  sensory  "  or  "  motor  "  area  change 
from  time  to  time.  Not  infrequently  they  appear  to  be 
almost  wholly  temporary.  Among  those  effects  that  seem 
to  be  permanent,  some  are  obviously  so ;  but  others  are  so 
delicate  as  almost  wholly  to  escape  observation.  It  is,  of 
course,  peculiarly  difficult  to  tell  just  what  is  the  nature 
of  an  animal's  sensory  activities ;  and  how  much  of  intel- 
lectual or  "psychical"  quality  is  lacking  to  its  hearing, 
smelling,  tasting,  feeling,  or  seeing. 

Evidence  from  Pathology.  —  It  is  pathology  which  gives 
us  the  most  direct  evidence  for  the  localization  of  cerebral 
function  in  the  case  of  man.  We  cannot  burn  or  cut  away 
portions  of  the  human  brain  merely  for  purposes  of  experi- 
ment. Yet  accident  and  disease  destroy  the  different 
areas  of  its  cortical  substance.  Such  lesions,  however,  are 
rarely  circumscribed  nicely  like  those  which  can  be  made 
in  the  brain  of  an  animal  by  the  knife  or  corroding  acid  of 
the  operator.  They  are  usually  accompanied  by  lesions  in 
the  sensory  and  motor  tracts  below  the  cortical  substance ; 
and  this  may  vitiate  the  conclusion  otherwise  to  be  derived 
from  them.  It  is  only  by  post-mortem,  as  a  rule,  that  the 
last  state  of  the  case  can  be  exactly  known.  And  the 
reports  of  post-mortem  cases  have  hitherto  —  owing  to  the 
ignorance  and  carelessness  about  such  matters  of  the  aver- 
age physician  —  been  so  lacking  in  precision  as  greatly  to 
embarrass  the  progress  of  science. 

The  evidence  from  pathology  has  thus  far  been  exceed- 
ingly conflicting.  Gradually,  however,  clearer  light  from 
this  source  has  been  shed  upon  the  important  question  of 
cerebral  localization.  Physicians  and  surgeons  are,  in 
general,  becoming  better  acquainted  with  the  more  impor- 
tant facts.  Even  now  it  is  possible  for  the  skilful  prac- 
titioner to  relieve  or  cure  certain  diseases  by  surgical  means 
directed  in  accordance  with  the  newly  discovered  truths 
of  cerebral  localization.  The  investigator  in  physiology  is, 


192  PHYSIOLOGICAL   PSYCHOLOGY. 

meantime,  accumulating  material  for  more  extended  and 
accurate  inductions. 

Evidence  from  Comparative  Anatomy  and  Histology.  — 
The  comparative  study  of  animal  structure,  combined 
with  experiment  by  electrical  irritation,  shows  that,  on  the 
whole,  the  "  excito-motor  areas  "  which  may  be  discovered 
on  the  hemispheres  of  the  brain  increase  in  number  and 
definiteness  with  the  increase  in  elaborateness  of  structure 
and  in  general  intelligence.  Only  traces  of  such  areas 
can  be  found  in  the  case  of  frog  or  pigeon ;  only  a  few 
areas  can  be  doubtfully  pointed  out  in  the  case  of  rat  or 
guinea-pig.  But  the  convolutions  of  the  brains  of  dogs 
and,  particularly,  of  the  man-like  apes,  are  much  more 
specialized  in  respect  to  function.  While  then  we  cannot 
approve  of  the  argument  which  transfers  the  map  of  so- 
called  "  centres  "  indicated  for  these  higher  animals  to  the 
cerebral  hemispheres  of  man,  we  admit  the  principle  that 
the  probability  of  a  correspondence  in  the  localization  of 
cerebral  function  increases  with  their  anatomical  likeness 
to  man.  Hence  the  superior  value  of  experiment  with  the 
brains  of  monkeys. 

As  histology  succeeds  in  tracing  the  connections  of  the 
different  areas  of  the  hemispheres  with  one  another,  and 
with  the  nerve-tracts  of  the  lower  parts  of  the  brain  and 
of  the  spinal  cord,  it  affords  evidence  confirmatory  or  cor- 
rective of  the  evidence  from  experimentation  and  pathol- 
ogy- 

Use  of   all  the    Evidence.  —  The   detailed  study  of  the 

problem  of  the  localization  of  cerebral  function  is  one  of 
the  most  stimulating  and  instructive  instances  of  the  use 
of  inductive  methods  to  disentangle  the  truth  from  a  con- 
fused mass  of  seemingly  conflicting  phenomena.  The 
proof  of  the  truth  must  combine  satisfactorily  the  evidence 
from  all  the  sources.  In  making  the  necessary  induction 
the  following  course  is,  in  our  judgment,  most  effective. 


SENSORY  AND  MOTOR   BRAIN   FUNCTIONS.  193 

The  indications  of  experiment  upon  the  cerebral  hemi- 
spheres of  the  animals  —  chiefly,  of  course,  those  most 
closely  allied  to  man  in  their  cerebral  structure  —  must 
first  be  gathered  and  carefully  weighed.  The  two  forms 
of  experimentation  —  stimulation  and  extirpation  —  should 
confirm  each  other,  in  order  to  give  the  surer  indications. 
Guided  by  these  indications  we  must  then  seek  light  from 
human  pathology.  All  accessible  pathological  cases  must 
be  sifted  and  those  only  selected  for  use  which  have  the 
definite  and  trustworthy  character  necessary  to  fit  them  for 
the  purposes  of  induction.  Especially  must  care  be  taken 
that  our  theory  do  not  neglect  the  consideration  of  negative 
cases  ;  and  even  of  those  cases  which  (in  themselves  con- 
sidered) furnish  indications  contradictory  of  the  great  body 
of  collected  cases.  The  corrective  or  confirmatory  evi- 
dence of  anatomy  and  histology  may  then  be  applied  to 
our  conclusions.  Only  when  all  the  lines  of  evidence 
unite  with  a  large  and  substantial  agreement,  if  not  with 
an  absolute  uniformity,  can  we  feel  the  highest  attainable 
confidence  in  our  results. 

The  Argument  from  Negative  Cases.  —  The  first  general 
principle,  to  be  admitted  in  all  attempts  at  a  theory  of  the 
localization  of  cerebral  function,  IL  of  a  negative  character. 
Considerable  areas  of  the  cortical  substance,  when  stimu- 
lated, do  not  occasion  any  movements  in  the  muscles  of 
the  body.  Considerable  portions  of  this  substance  may  be 
destroyed  and  no  appreciable  loss  or  disturbance  of  any 
motor,  sensory,  or  intellectual  activities  result.  The  early 
researches  of  Fritsch  and  Hitzig  pointed  out  only  five 
spots  —  each  one  of  a  small  fraction  of  an  inch  in  diameter 
(2-3  mm.,  as  a  rule)  —  that  could  be  definitely  related  to 
the  movement  of  certain  groups  of  muscles.  Between  and 
around  these  areas  lay  the  much  larger  areas  of  negative 
result.  Though  the  number  of  irritable  spots  on  the  hemi- 
spheres of  the  brains  of  the  higher  animals  has  since  been 


194  PHYSIOLOGICAL   PSYCHOLOGY. 

considerably  increased,  the  non-irritable  portions  still  re- 
main greatly  in  the  predominance. 

Large  portions  of  the  cortical  substance  from  the  brain 
of  an  animal  may  be  removed  without  the  operation  being 
followed  by  the  permanent  and  complete  loss  of  any  func- 
tion, motor  or  sensory.  Indeed,  a  few  eminent  observers 
still  maintain  that  the  nature  and  extent  of  the  psychical 
disturbance  are  largely  or  wholly  independent  of  the  local- 
ity from  which  the  brain  substance  is  taken. 

The  negative  evidence  from  certain  cases*  in  human 
pathology  is  even  more  remarkable.  There  are  recorded 
many  instances  of  large  lesions  in  the  cerebral  hemispheres 
of  man  with  little  or  no  resulting  mental  disturbance. 
One  authority  tells  of  a  young  man  who  had  a  foreign 
body  of  four  fingers'  breadth  square  buried  in  his  brain, 
and  yet  lived  for  a  long  time  afterward  in  the  enjoyment 
of  all  his  faculties.  Another  communicates  the  case  of  an 
Italian  laborer  whose  skull  was  crushed,  in  the  right 
parietal  region,  by  a  stone.  This  patient  subsequently  lost 
so  much  of  the  substance  of  the  brain  that  it  was  calcu- 
lated the  lesion  must  extend  down  to  the  corpus  callosum. 
He,  too,  lived  without  mental  impairment;  but  with  a 
laming  of  the  limbs  on  the  left  side. 

Other  remarkable  cases  of  lesion  of  the  brain,  followed 
by  little  or  no  loss  of  psychical  functions,  are  such  as  this : 
A  man  whose  skull  was  crushed  with  a  stone,  and  whose 
entire  left  hemisphere  (on  his  death  twenty  days  later) 
was  found  to  be  a  disorganized  mass,  continued  in  appar- 
ently full  possession  of  his  powers  of  motion,  sensation, 
and  intelligence.  Instances  of  defective  brains  are  also  on 
record.  In  one  such  case,  the  place  of  the  right  hemi- 
sphere was  discovered  to  have  been  filled  with  a  serous 
fluid.  No  peculiarities  of  this  person's  mental  life  were 
noticed ;  but  there  had  been  from  birth  lameness  of  the  left 
side  of  the  body. 


SENSORY  AND   MOTOR   BRAIN   FUNCTIONS.  195 

Extensive  lesions  without  marked  disturbance  of  the 
motor  or  sensory  functions  are  especially  frequent  in  the 
frontal  lobes.  They  occur,  however,  not  very  infrequently 
in  the  occipital  and  temporo-sphenoidal  lobes.  A  case  is 
recorded  of  an  officer  shot  through  the  middle  of  the  fron- 
tal lobes,  who  till  death  showed  no  signs  of  any  kind  of 
paralysis.  The  work  of  M.  Pitres  contains  a  large  collec- 
tion of  cases  in  which  these  lobes  have  been  the  seat  of 
extensive  disease,  without  any  symptoms  of  lunacy  or  of 
psychical  disturbance.  The  so-called  "  American  crowbar 
case "  is  well  known.  An  iron  bar,  3  feet  7  inches  in 
length  and  1J  inches  in  diameter,  passed  entirely  through 
the  top  of  a  man's  head,  near  the  sagittal  suture  in  the 
frontal  region.  But  the  patient  recovered  in  a  few  min- 
utes so  as  to  ascend  a  flight  of  stairs  and  give  to  the  sur- 
geon an  intelligible  account  of  his  injury.  He  lived 
twelve  and  a  half  years  afterward,  with  no  noticeable 
impairment  of  his  sensory  or  motor  powers. 

In  the  words  of  a  distinguished  physiologist,  it  must  be 
confessed  that  the  understanding  of  cases  like  those  just 
mentioned  "  is  made  more  difficult  rather  than  easier  by 
recent  researches."  The  evidence  of  these  negative  cases 
is,  indeed,  quite  too  much  neglected  by  those  who  make 
haste  to  erect  on  insufficient  data  a  plausible  theory. 
Indeed,  the  general  fault  of  writers  on  the  localization  of 
cerebral  functions  is  that  they  consider,  as  a  rule,  only  the 
cases  which  suggest  or  confirm  their  theory ;  while  they 
neglect  those  even  more  important  negative  cases  which 
tend  to  refute,  correct,  or  modify  the  theory. 

And  yet,  a  large  amount  of  concurrent  testimony  from 
all  these  main  sources  of  evidence  warrants  us  in  announc- 
ing certain  positive  results.  A  science  of  the  localization 
of  cerebral  functions,  in  some  justifiable  meaning  of  these 
words,  may  be  said  to  be  fairly  defined. 


CHAPTER   IX. 

SENSORY  AND    MOTOR    FUNCTIONS   OF    THE    CERE- 
BRAL  HEMISPHERES.  —  Continued. 

THE  region  of  the  brain  which  is  especially  concerned 
with  the  motor  functions  lies  about  the  great  central  fis- 
sure, or  Fissure  of  Rolando.  More  precisely,  it  embraces 
the  ascending  frontal  convolution  (jgyrus  centralis  ante- 
rior), the  ascending  parietal  (the  gyrus  centralis  posterior), 
and  the  prolongation  of  the  two  on  the  median  surface  of 
the  brain  (in  the  lobulus  paracentralis). 

LOCALIZATION  OF  THE  MOTOR  CENTRES  ON  THE 
CEREBRAL   CORTEX. 

Areas  excitable  by  Stimulation.  —  The  original  experi- 
ments of  Fritsch  and  Hitzig  located  five  areas  on  the  cere- 


FIG.  63.  —  Hitzig's  Motor  Areas  on  the  Cortex  of  the  Dog.  The  left  hemisphere 
belongs  to  one  animal,  the  right  to  another;  a,  the  sulcus  cruciatus,  around  which  the 
gyrus  sigmoideus  bends;  0000,  area  for  the  face.  The  other  symbols  are  explained  in 
the  text. 

196 


SENSORY  AND   MOTOR   BRAIN  FUNCTIONS.  197 

bral  hemispheres  of  the  dog,  which  responded  to  irritation 
with  the  movement  of  definite  groups  of  muscles.  They 
were  (1)  the  centre  for  the  muscles  of  the  neck  (A  in  the 
Fig.)  ;  (2)  the  centre  for  the  extensor  and  adductor  of  the 
fore-limb  (-H-)  ;  (3)  the  centre  for  the  bending  and  rota- 
tion of  the  same  limb  (+) ;  (4)  the  centre  for  the  hind- 
limb  (#) ;  and  (5)  the  facial  centre  (0  -  0).  These 
investigators  also  obtained  contractions  of  the  muscles  of 
the  back,  tail,  and  abdomen  by  stimulating  interlying 
points,  but  failed  definitely  to  circumscribe  areas  for  these 
muscles. 

The  accompanying  figure  (No.  64)  shows  the  numerous 
"  centres    of    electrical    miration,"    which    Dr.    Ferrier 


FIG.  64.  — Areas  on  the  Left  Hemisphere  of  the  Monkey,  by  stimulating  \vhich  Ferrier 
obtains  motion  in  definite  groups  of  muscles. 

claimed,  some  six  years  later,  to  have  discovered  on  the 
cerebral  hemispheres  of  the  monkeys  with  which  he  has 
experimented.  It  will  be  noticed  that  these  centres,  like 
those  discovered  in  dogs  by  the  two  German  explorers,  lie 
around  the  great  central  fissure,  known  in  the  human 
brain  as  the  Fissure  of  Rolando. 

Recent  experiments  in  the  attempt  to  establish  motor 
centres  by  electrical  stimulation  tend  to  confirm  the  gen- 
eral conclusion.  Some,  however,  have  claimed  that 


198  PHYSIOLOGICAL   PSYCHOLOGY. 

changes  in  the  excitability  of  these  minute  areas  take 
place ;  that  certain  ones,  at  first  excitable,  after  a  time 
cease  to  be  so,  and  that  others,  at  first  not  excitable,  after- 
ward become  excitable.  Very  suggestive  is  the  further 
alleged  discovery  that  a  number  of  minute  areas  for  each  one 
of  several  different  groups  of  muscles  exist  in  the  larger 
"  excitable  zone  "  of  the  cortex.  The  fibres  whose  func- 
tion it  is  to  contract  these  groups  of  muscles  would  seem 
then  to  proceed  directly  from  a  number  of  cerebral  spots 
belonging  to  each  group.  These  minute  areas  for  the 
different  muscles  of  the  extremities  are  said  to  be  limited 
with  great  sharpness ;  they  do  not  wholly  cover  each 
other;  and  those  for  any  particular  muscle  are  of  small 
extent  in  comparison  with  the  field  or  zone  which  may  be 
looked  upon  as  common  to  all  the  extremities. 

The  Extirpation  of  "  Motor  Centres."  —  As  a  rule,  the  de- 
struction of  those  areas  of  the  cerebral  hemispheres,  from 
which  co-ordinated  movement  of  definite  groups  of  muscles 
can  be  excited  by  stimulation,  causes  a  temporary  or  per- 
manent impairment  in  the  use  of  the  same  muscles.  Thus 
the  evidence  of  extirpation  confirms,  in  a  general  way,  the 
evidence  from  stimulation.  The  pioneer  investigators, 
Fritsch  and  Hitzig,  removed  from  two  dogs  the  substance 
of  the  centre  which  they  had  fixed  upon  as  that  for  the 
"  right  fore  extremity."  They  observed  that  these  animals 
afterward  used  the  right  fore-leg  unskilfully.  Since  that 
time  many  observers  have  refined  and  multiplied  this  class 
of  experiments  in  the  localizing  of  the  motor  functions  of 
the  hemispheres.  We  now  refer  to  some  of  the  results 
thus  obtained. 

Experiments  of  Munk.  —  This  investigator  experimented, 
at  first,  by  removing  clean-cut  circular  bits  about  f  of  an 
inch  in  diameter  and  -^  of  an  inch  thick  from  the  convex 
surfaces  of  the  parietal,  occipital,  and  temporal  lobes  of 
dogs.  His  general  conclusion  was  as  follows  :  If  a  line  be 


SENSORY  AND   MOTOR   BRAIN   FUNCTIONS. 


199 


drawn  from  the  terminal  point  of  the  Fissure  of  Sylvius 
vertically  toward  the  falx  cerebri,  it  will  approximately 
mark  out  the  limits  of  an  anterior  motor  and  a  posterior 
sensory  sphere. 


FIG.  65.  — Areas  on  the  Brain  of  the  Dog.  (According  to  Munk.)  A,  centre  of  the 
Eye;  JS,  of  the  Ear;  C,  of  the  sensations  of  the  hind-leg;  D,  of  the  fore-leg;  E,  of 
the  Head;  F,  of  the  Apparatus  for  protecting  the  Eye;  G,  of  the  Region  of  the  Ear; 
ff,  of  the  Neck;  J,  of  the  Rump. 

Munk's  attempts  at  more  precise  localization  are  indi- 
cated in  the  accompanying  figure  (No.  65).  It  will  be 
noticed  that  three  of  these  centres —  (7,  D,  and  E — 
correspond  fairly  well  with  those  fixed  upon  by  the  first 
experimenters  in  stimulation.  In  the  regions  indicated  on 
the  chart,  Munk  claimed  to  find  that  small  and  definitely 


200 


PHYSIOLOGICAL   PSYCHOLOGY. 


circumscribed  extirpations  are  regularly  followed  by  defi- 
nitely localized  disturbances  of  motion. 

For  example,  let  the  region  D  be  removed  from  the  left 
hemisphere  of  the  brain  of  a  dog.  Then  if  any  other  of  the 
animal's  limbs  be  ever  so  lightly  touched,  he  will  heed  it;  but 
hard  pressure,  pinching,  and  sticking  of  the  right  fore-leg  is 
either  followed  by  no  result,  or  by  what  seems  to  be  only 
the  reflex  withdrawal  of  the  leg,  without  attention.  More- 
over, the  dog  will  suffer  this  limb  to  be  placed  in  awkward 
and  uncomfortable  positions.  He  no  longer  handles  his 
food  with  the  right  foot,  and  does  not  give  this  limb  to  his 
master  on  call.  In  running  he  slips  on  this  foot.  These 
and  other  phenomena  led  this  investigator  to  hold  that  the 
animal  had  lost  the  "  cerebral "  or  intelligent  quality  from 
the  management  of  this  limb,  and  perhaps  had  no  mental 
picture  of  it  in  mind. 

Experiments  of  Horsley  and  Schafer.  —  The  value  of  ex- 


FIG.  66.  —  Lateral  Surface  of  Brain  of  Monkey.     (Taken  from  "  Brain.") 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS* 


201 


periments  by  way  of  stimulation  and  extirpation  upon  the 
cerebral  hemispheres  of  the  monkey  is,  on  account  of  the 
resemblance  of  this  animal's  brain  to  that  of  man,  undoubt- 
edly very  great.  Among  the  latest  physiological  researches 
bearing  on  the  localization  of  motor  centres  in  the  cere- 
brum, perhaps  none  are  more  important  than  those  of  the 
two  investigators  whose  names  head  this  paragraph.  Their 
conclusions  are  represented  in  the  accompanying  diagrams 
(Figs.  66  and  67).  It  must  be  understood,  however,  that  all 


FIG.  67.  —  Median  Surface  of  Brain  of  Monkey.     (Taken  from  "  Brain.") 

the  so-called  "  motor  centres "  marked  on  these  diagrams 
have  not  the  same  evidence  in  their  favor.  Some  of  them 
await  further  experimental  evidence.  A  warning  must 
also  be  uttered  against  attempting  to  copy  this  provisional 
chart  off,  unchanged,  upon  the  map  of  the  human  brain. 

Interpretation  of  the  Phenomena.  —  The  meaning  of  the 
apparent  loss  of  the  animal's  functions  through  extirpation 


202  PHYSIOLOGICAL  PSYCHOLOGY. 

of  the  so-called  "motor  centres"  is  not  perfectly  clear. 
It  will  always  be  difficult  to  designate  precisely  what  fac- 
tors in  the  complex  sensory-motor  activities  of  a  dog  or  a 
monkey  drop  out  as  the  result  of  removing  a  certain  area 
of  its  cortical  substance.  Several  explanations  of  such 
phenomena  of  motor  disturbance  are  possible.  It  may  be 
held,  in  the  first  place,  that  the  extirpated  centres  are 
exclusively  motor ;  they  are,  that  is,  the  areas  in  which 
alone  can  originate  the  different  efferent  impulses  to  the 
groups  of  muscles  that  move  the  limbs.  The  only  impair- 
ment of  functions  is,  then,  the  loss  of  connection  between 
the  "projection-fibres"  and  the  cerebral  substance  which 
controls  them. 

But  others  hold  that  the  real  loss  of  function  in  these 
cases  is  sensory  rather  than  motor.  The  disturbance  or 
loss  of  motion  is,  then,  only  the  expression  of  a  loss  of  the 
sense  of  touch  in  the  parts  to  be  moved.  In  other  words, 
it  is  "tactile  ansesthesia."  In  proof  of  this  conclusion, 
attention  is  called  to  the  fact  that  an  animal  thus  operated 
upon  will  allow  parasites  to  gather  on  that  surface  of  the 
skin  whose  cortical  area  has  been  removed.  The  inability 
of  the  animal  to  use  its  extremities  as  hands  may  also  be 
assigned  to  a  loss  of  those  finer  sensibilities  which  guide 
such  movements. 

Or,  again,  the  impairment  of  function  may  be  regarded 
as  largely  due  to  the  loss  of  power  to  hold  before  the  mind 
a  picture  of  the  limbs,  and  of  the  movements  which  it  is 
desirable  to  excite.  This  would  seem  to  indicate  injury  to 
the  animal's  general  psychical  quality,  and  might  involve 
both  the  sensory  and  the  motor  factors.  The  importance 
of  the  "  association-fibres "  in  these  cortical  centres  is 
beyond  doubt.  For  if  the  centres  be  carefully  cut  round 
so  as  to  sever  these  fibres,  but  not  the  "  projection-fibres," 
their  loss  of  function  is  almost,  if  not  quite,  as  great.  In 
fact,  all  the  disturbances  —  whether  sensory  or  motor — ap- 


SENSORY   AND    MOTOR   BRAIN   FUNCTIONS.  203 

pear  to  be  of  the  kind  which  indicates  loss  of  cerebral,  and 
so  of  psychical  quality  in  the  handling  of  the  extremities, 
rather  than  the  laming  of  any  particular  group  of  muscles. 
Indeed,  one  principal  authority  (Goltz)  still  insists  that 
the  general  impairment  of  intelligence  which  results  from 
removing  any  considerable  amount  of  brain-substance, 
from  whatever  area  it  is  taken,  constitutes  the  most 
marked  feature  of  all  these  cases.  He  finds  that,  although 
impairment  of  both  tactile  and  muscular  sense  may  tem- 
porarily occur,  yet  the  animal  by  giving  "  increased  atten- 
tion "  is  able  to  feel  the  slightest  touch  on  any  area  of  the 
skin. 

In  view  of  all  the  evidence,  our  provisional  conclusion 
may  be  expressed  as  follows :  Certain  areas  of  the  brains 
of  the  lower  animals,  especially  of  the  dog  and  monkey, 
have  a  special  value  and  use  in  the  control  of  the  muscles 
of  the  body.  These  areas  are  situated  in  that  region  of 
the  cortex  which  corresponds,  in  man,  to  the  convolutions 
on  either  side  of  the  Fissure  of  Rolando,  and  to  the  adja- 
cent lobule  (lobulus  paracentralis)  on  the  median  surface  of 
the  brain.  The  loss  or  disturbance  of  motor  function  which 
follows  injury  to  these  areas  is  often  due  to  complex  men- 
tal disturbances.  These  are  partly  sensory,  —  impairment 
of  the  nicely  shaded  tactile  and  muscular  sensations  by 
which  the  animal  guides  its  limbs ;  partly  motor,  —  impair- 
ment of  power  to  execute  the  volition,  or  realize  in  actual 
movement  the  mental  picture  of  the  movement  and  the 
desire  to  move ;  partly  more  purely  psychical,  — impairment 
of  power  to  form  complex  mental  images  of  the*  specific 
sort  required,  and  of  mental  ability  to  take  an  interest  in 
or  to  comprehend  complex  objects  and  situations. 

In  the  case  of  the  higher  animals  (and  especially  of  the 
monkey),  a  further  discrimination  of  these  areas  may  be 
attempted  with  some  success.  Localization  of  the  con- 
nected sensory  and  motor  factors  in  these  complex  activi- 


204  PHYSIOLOGICAL   PSYCHOLOGY. 

ties  places  the  former  more  to  the  rear,  and  the  latter  more 
to  the  front,  of  this  general  area.  What  is  true  of  the  gen- 
eral area  is  perhaps  true  of  the  particular  areas  into  which 
the  general  area  may  be  divided.  The  broader  outlines  of  the 
diagrams  prepared  by  Horsley  and  Schafer  (see  p.  200  f .) 
may  be  taken  as  indicating  to  human  pathology  its  partic- 
ular problems. 

Our  reliance  must  now  be  placed  upon  Human  Pathology. 
And  although  much  has  been  done  by  others  in  the  nearly 
ten  years  since  Exner's  work  appeared,1  the  thoroughness 
and  carefulness  of  his  induction  entitles  it  to  be  still  con- 
sidered as  representative  of  the  most  trustworthy  conclu- 
sions. 

Exner's  Induction  of  the  Motor  Areas  in  Man.  —  The  con- 
clusions of  this  authority  were  based  upon  researches  into 
several  thousand  cases  of  cerebral  disease  which  had  been 
followed— by^^jpst-mortem  examination.  From  this  large 
number,,  169  "test-cases"  were  selected.  In  all  these  cases 
the  record  was  trustworthy,  full,  and  unambiguous ;  and 
no  other  lesions  than  the  one  in  some  particular  cortical 
area  had  occurred  to  complicate  the  inferences.  The  test- 
cases  were  tabulated  on  three  sets  ef  maps,  according  to 
three  methods  of  induction :  (1)  Method  of  negative  cases ; 
(2)  method  of  percentage^  (3)  method  of  positive  cases. 
Thus  the  first  map  showed  what  areas  of  the  cerebral  cor- 
tex, if  any,  are  not  necessarily  connected  with  motor  or 
sensory  functions.  The  second  map  showed  the  amount 
of  probability  that  a  given  small  area  will  be  the  seat  of 
disease,  in  case  this  disease  has  been  followed  by  a  given 
kind  of  sensory  or  motor  disturbance.  [For  this  purpose 
the  map  was  divided  into  367  small  quadrilateral  sections.] 
The  third  map  simply  tabulated  the  cases  of  lesions  actu- 

1  Investigation  into  the  Localization  of  Function  in  the  Cerebral  Hemi- 
spheres of  Man.  Vienna,  1881, 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS. 


205 


ally  connected  with  observed  disturbances  of  function,  in 
the  spots  on  the  cortex  where  they  occurred. 


FIG.  68.  — Lateral  View  of  the  Human  Brain.  (Schematic,  Ecker.)  F,  frontal, 
P,  parietal,  O,  occipital,  and  T,  ternporo-sphenoidal  lobes.  8,  fissure  of  Sylvius,  with 
8',  the  horizontal,  and  S",  the  ascending  ramus;  C,  sulcus  central!*;  A,  anterior,  and 
B,  posterior,  central  convolutions;  Fl,  F2,  F3,  superior,  middle,  and  inferior  frontal  con- 
volutions; ft,  superior,  f2,  inferior  frontal  sulcii  f3,  sulcus  praecentralis;  PI,  superior, 
and  P2,  inferior  parietal  lobule;  the  latter,  the  gyrus  supra-marginalis,  and  P2',  the 
gyrus  angularie;  ip,  sulcus  inb^rp^arietalis;  cm,  end  of  calloso-marginal  fissure;  Ol,  O2, 
OS,  occipital  convolutions;  po,  parieto-occipital  fissure;  o,  transverse,  and  o2,  inferior 
longitudinal  sulcus;  Tl,  T2,  T3,  temporo-sphenoidal  convolutions;  and  tl,  12,  tempero- 
sphenoidal  fissures. 

Field  of  Latent  Lesions,  —  In  Exner's  collection  of  cases, 
20  were  found  in  each  hemisphere  which  had  been  followed 
by  no  disturbances  whatever,  whether  of  motion  or  of  sen- 
sation. But  since  the  collection  comprised  101  lesions  of 
the  left  hemisphere,  and  only  67  of  the  right,  it  will  be 
seen  that  the  chances  of  a  lesion  being  latent  (i.e.  resulting 


206 


PHYSIOLOGICAL   PSYCHOLOGY. 


in  no  disturbance  of  function)  are  much  greater  for  the 
right  than  for  the  left  hemisphere.  On  the  right  hemi- 
sphere the  entire  surface,  with  the  exception  of  the  two  cen- 
tral convolutions,  the  paracentral  lobule,  and  small  portions 
of  the  convex  and  inferior  surfaces  of  the  occipital  lobe,  is 


FIG.  69.  —  View  of  the  Human  Brain  from  Above.     (Schematic,  Ecker.)     The  letters 
have  the  same  reference  as  in  the  preceding  figure. 

latent.  On  the  left  hemisphere  the  latent  field  is  much 
less  extensive.  This  result  of  the  induction  restates  the 
well-known  fact  that  extensive  lesions  frequently  occur 
in  the  frontal,  temporal,  and  occipital  lobes,  without  occa- 
sioning any  noticeable  motor  or  sensory  disturbance. 


SENSORY  AND  MOTOR   BRAIN   FUNCTIONS. 


207 


The  regions  not  latent  Exner  divided  into  "  absolute 
fields  "  (or  areas  within  which  no  lesion  occurred  without 
the  expected  result)  and  "  relative  fields "  (or  areas  in 
which  more  than  fifty  per  cent,  of  the  cases  of  lesion 
resulted  in  a  disturbance  of  function). 

Fields  of  the  Upper  Extremities.  —  Exner's  induction  from 
the  test-cases  seemed  to  show  that  the  "absolute  field" 
for  the  upper  extremity  on  the  right  hemisphere  (i.e.  field 
for  the  left  arm)  includes  the  paracentral  lobule,  the  ante- 
rior central  convolution  (with  the  exception  of  a  small 

A.     9 


FIG.  70.— Median  Aspect  of  the  Right  Hemisphere.  (Schematic,  Ecker.)  CO,  cor- 
pus  callosum.  Gyri:  Gf,  fornicatus;  H,  hippocampi  (with  its  sulcus  h),  and  U,  uncina- 
tus;  PI',  prascuneus;  Oz,  cuneus;  oc,  calcarine  fissure,  with  its  two  rami  oc'and  oc". 
D,  gyrus  descendens;  T4,  the  lateral,  and  T5,  the  medial,  gyrus  occipito-temporalis. 

part  of  its  lower  end),  and  the  upper  half  of  the  posterior 
central  convolution.  The  "relative  field"  for  the  same 
extremity  extends  further,  and  includes  the  back  part  of 
the  three  frontal  convolutions,  the  front  part  of  the  parietal 
lobe,  and  a  considerable  part  of  the  neighboring  median 
surface. 

On  the  left  hemisphere  the  fields  for  the  upper  extrem- 


208  PHYSIOLOGICAL  PSYCHOLOGY. 

ity  (i.e.  the  right  arm)  are  more  extended.  Here  the 
"  absolute  field  "  extends  over  the  greater  part  of  the  upper 
parietal  lobe ;  and  perhaps  over  portions  of  the  median 
surface  of  the  occipital  lobe.  The  "relative  field"  com- 
prises a  yet  larger  area  of  this  general  region  of  the  brain. 
All  this  corresponds  to  the  fact  that,  in  the  great  majority 
of  men,  the  right  hand  and  arm  are  more  employed  for  the 
discharge  of  delicate  and  highly  intelligent  functions,  and 
therefore  require  a  larger  cerebral  assistance  and  control. 

Fields  of  the  Lower  Extremities. — Exner's  induction 
points  out,  as  the  "  absolute  field  "  on  the  right  hemisphere 
for  the  lower  extremity  (i.e.  the  left  leg),  the  paracentral 
lobule,  the  upper  third  of  the  anterior  central  convolution, 
parts  of  the  corresponding  third  of  the  posterior  central, 
and  some  small  areas,  behind  and  below,  on  the  lobulus 
quadratus.  The  "  relative  field "  of  the  same  limit  is,  of 
course,  larger.  On  the  left  hemisphere  the  "absolute 
field"  includes  also  most  of  the  upper  portion  of  the 
parietal  lobe. 

The  lower  extremities  can  scarcely  have  the  functions 
of  their  different  parts  localized  with  the  same  degree  of 
precision  and  amount  of  differentiation  which  belong  to  the 
upper  extremities.  This  fact  corresponds  to  the  relatively 
low  cerebral  and  psychical  character  of  their  sensations 
and  motions.  More  of  the  '^rain  and  mind  is  required  for 
the  control  of  the  arms  than  of  the  legs. 

General  Motor  Region  in  Man.  —  The  "exquisitely  mo- 
tor "  region  of  the  human  cerebral  cortex  lies,  then,  around 
the  Fissure  of  Rolando  and  in  the  paracentral  lobule.  It 
reaches  over,  in  a  somewhat  indefinite  way,  into  the  adja- 
cent parts  of  the  frontal  and  parietal  lobes.  Besides  the 
"  m<3tor  areas  "  of  the  extremities,  those  for  the  muscles  of 
the  eyeball,  tongue,  head,  and  neck  are  in  this  same  gen- 
eral region.  For  example,  in  nine  cases  of  Exner's  collec- 
tion, in  which  the  muscles  of  head  and  neck  were  affected, 


SENSOKY   AND   MOTOR   BRAIN   FUNCTIONS.  209 

the  lesions  were  all  situated  in  one  of  the  two  central  con- 
volutions. 

There  can  be  no  reasonable  doubt,  therefore,  that  the 
general  indications,  which  were  said  to  be  derived  from 
experiments  with  the  dog  and  the  monkey,  are  confirmed 
by  human  pathology.  As  two  celebrated  investigators 
(Charcot  and  Pitres)  have  summed  up  the  evidence : 
"  The  cortex  of  the  cerebral  hemispheres  in  man  may  be 
divided,  functionally,  into  two  parts,  motor  and  non- 
motor,  according  as  destructive  lesions  do  or  do  not  cause 
permanent  paralysis  on  the  opposite  side  of  the  body. 
.  .  .  The  motor  zone  includes  only  the  ascending  frontal 
and  ascending  parietal  convolutions  and  the  paracentral 
lobule." 

Further  Specialization  of  Motor  Areas,  —  More  specific 
statements  as  to  the  localization  of  functions  for  small 
parts  of  the  extremities,  or  even  for  particular  groups  of 
muscles,  cannot  be  made  with  the  same  confidence.  Clin- 
ical and  surgical  evidence  is  accumulating,  however.  For 
example,  a  case  is  reported,  definitely  connecting  spasms 
beginning  in  the  right  lower,  u  d  extending  to  the  right 
upper,  limb  and  to  the  face,  with  a  lesion  in  the  upper 
third  of  the  ascending  frontal  convolution  on  the  left  side ; 
and  another  case,  connecting  cramps  in  the  left  thumb  and 
fore-finger,  spreading  up  the  L.,m,  with  a  tumor  situated  at 
the  line  of  the  junction  of  the  lower  and  middle  thirds  of 
the  ascending  frontal  and  parietal  convolutions. 

One  authority  (Horsley)  divides  the  "  arm  area "  as 
follows :  for  the  shoulder,  in  the  upper  part ;  the  elbow, 
next  below  and  behind;  the  wrist,  next  below  and  in 
front;  the  thumb,  lowest  and  behind.  In  the  area  just 
above  the  superior  frontal  sulcus,  he  thinks  that  the  move- 
ments of  the  lower  and  upper  limbs  are  blended.  Another 
authority  (Dr.  Mills)  thinks  that  "  instead  of  dividing  the 
central  or  Rolandic  Fissure  into  thirds,  it  is  better,  perhaps, 


210 


PHYSIOLOGICAL   PSYCHOLOGY. 


to  divide  it  into  fourths,  placing  the  area  of  representation 
for  the  lower  extremity  in  the  first  fourth ;  that  of  the 
face  in  the  lower  fourth;  and  the  area  for  the  upper 
extremity  includes  the  second  and  third  fourths." 


FIG.  71.  —  Areas  of  the  Mesial  Aspects  of  the  Cerebrum.     (Taken  from  "  Brain.") 


The  accompanying  diagrams  (71  and  72)  may  be  said 
to  represent  the  most  advanced  views  in  the  localization 
of  cerebral  motor  functions  in  man.  For  this  very  reason, 
and  because  they  are  based  only  upon  "positive  cases," 
instead  of  upon  an  induction  taking  also  the  "negative 
cases  '  into  the  account,  they  should  be  received  in  a  cau- 
tious and  tentative  way. 

Localization  of  Sensations  of  the  Skin  and  Muscles.  —  There 
is  considerable  evidence  to  show  that  the  regions  called 
"motor"  are  also  the  principal  seats  of  those  lesions  of 
the  cerebral  cortex  which  result  in  loss  of  the  sensations  of 
touch  (tactile  anaesthesia)  and  of  muscular  sensations. 


SENSORY  AND  MOTOR   BRAIN  FUNCTIONS. 


211 


This  has  led  some  to  hold  that  the  so-called  "motor"  areas 
are  the  central  representatives  of  the  sensory  impulses 
which  originate  in  the  skin  and  muscles  of  the  same  limb 


FIG.  72.  —  Areas  of  the  Lateral  Aspect  of  the  Cerebrum,  and  Sub-divisiona  of  the 
Motor  Area.     (Taken  from  "  Brain.") 


which  is  moved  from  these  areas.  For  the  conception  of 
"sensory  and  motor  centres,"  therefore,  one  authority 
would  substitute  the  conception  of  excitable  cortical  areas 
reacting  after  the  manner  of  sensitive  peripheral  surfaces  : 
the  true  motor  centres  lie  below.  We  have  already  seen 
(p.  67)  that  histology  has  attempted  to  distinguish  motor 
and  sensory  cells  in  the  same  layer,  or  motor  and  sensory 
layers  in  the  same  area,  of  the  cortical  substance.  The 
distinction  is  not,  however,  as  yet  established. 


212  PHYSIOLOGICAL  PSYCHOLOGY. 

Human  pathology  has  not  yet  succeeded  in  assigning  an 
"  absolute  field  "  for  tactile  sensations.  There  is  no  portion 
of  the  cerebral  cortex  where  lesions  are  invariably  and 
necessarily  followed  by  disturbances  of  these  sensations. 
Exner's  induction  included  22  cases  of  marked  disturbance 
of  tactile  sensations.  Of  these  16  were  located  wholly  in 
the  two  central  convolutions,  and  3  others  partly  in  the 
same  convolutions.  The  percentage  of  such  cases  arising 
from  injury  to  the  right  hemisphere  is  about  twice  as 
large  as  that  of  the  left.  This  has  led  some  to  conclude 
that  sensibility  is  the  predominating  function  of  the  right 
hemisphere,  as  motion  is  of  the  left. 

The  psychical  relations  between  disturbances  of  motor 
function  and  disturbances  of  tactile  and  muscular  sensation 
are  undoubtedly  very  complex.  Physiology  has  not  yet 
unravelled  the  corresponding  cerebral  relations.  Perhaps 
we  cannot  do  better  than  to  conclude  with  one  writer : 
There  is  probably  a  general  region  for  sensations  of  touch, 
pain,  temperature,  pressure,  etc.,  of  the  peripheral  parts, 
and  this  region  is  divisible  into  minuter  areas ;  these  areas 
have  close  anatomical  and  morphological  relations  with  the 
corresponding  motor  areas,  but  are  probably  not  always 
wholly  identical  with  them.  So  far  as  the  two  regions  are 
not  coincident,  that  mainly  appropriated  to  sensory  func- 
tions lies  further  back.  It  perhaps  includes  the  •  gyrus 
fornicatus,  the  hippocampal  convolution,  the  pre-cuneus, 
and  the  postero-parietal  convolutions. 

LOCALIZATION  OF  THE  SENSORY   CENTRES    OF    THE   CERE- 
BRAL  CORTEX. 

It  requires  no  argument  to  shoAV  that  experiment  upon 
the  lower  animals  is  relatively  of  little  value  in  determin- 
ing the  cerebral  sensory  centres  in  man.  Localization  of 
"  sensory  centres  "  so-called  is  in  general  more  difficult  on 
account,  partly,  of  the  greater  complexity  of  the  psychical 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS.  213 

phenomena  and  of  the  physical  apparatus  concerned.  In 
particular,  it  is  almost  impossible  to  tell  with  confidence 
what  are  the  psychical  experiences,  the  sensory  states  of 
consciousness,  of  an  injured  dog  or  monkey.  Yet  by  com- 
bining with  experimentation  the  carefully  sifted  evidence 
of  human  pathology,  the  areas  of  the  brain-cortex  con- 
cerned in  vision  have  been  localized  with  approximate 
accuracy. 

Centre  of  Sight  according  to  Ferrier.  —  In  the  earlier  edi- 
tion of  his  work  on  the  "Functions  of  the  Brain"  this 
investigator  claimed  that  destruction  of  the  gyrus  angularis 
(see  Fig.  68)  produces  loss  of  sight  in  the  opposite  eye  ; 
while  stimulation  of  the  same  region  produces  movements 
of  the  eye.  In  a  subsequent  edition  Dr.  Ferrier  has  ad- 
mitted his  error  in  localizing  the  visual  centres  in  this 
convolution  to  the  exclusion  of  the  occipital  lobes.  And 
further  investigation  seems  to  have  shown  that  the  gyrus 
angularis  can  be  removed  without  any  permanent  effect 
whatever  upon  the  sense  of  sight. 

Centre  of  Sight  according  to  Munk.  —  This  investigator 
details  the  following  among  other  phenomena  which  result 
from  extirpation  of  the  region  marked  Al,  (see  Fig.  65,) 
from  the  brain  of  a  dog.  The  animal  may,  in  general,  be 
said  to  exhibit  marked  symptoms  of  "  psychical  blindness." 
By  this  term  it  is  meant  to  say  that  the  dog  cannot  form 
the  visual  images  or  ideas  which  give  meaning  to  the  visual 
impressions.  It  will  guide  itself  by  sight,  even  under 
difficult  circumstances.  But  it  does  not  recognize  the  dish 
from  which  it  has  been  accustomed  to  take  food,  the  man 
who  has  been  its  keeper,  the  threatening  whip  or  coal  of 
fire.  If  only  a  small  area  of  the  brain's  substance  is  re- 
moved, it  recovers  psychical  sight  by  again  learning  the 
meaning  of  its  visual  impressions.  Extirpation,  however, 
of  the  cortical  surface  somewhat  widely  around  Al,  in 
connection  with  this  concentrated  centre  itself,  results 


214  PHYSIOLOGICAL  PSYCHOLOGY. 

(when  both  hemispheres  are  involved)  in  complete  and 
permanent  "  psychical  blindness."  Similar  phenomena  are 
obtained  by  Munk  through  experimenting  upon  monkeys. 
He  concludes,  therefore,  that  a  large  part  of  the  convex 
surface  of  the  occipital  lobes  is  the  seat  of  perceptions  (?) 
of  sight ;  but  the  visual  memory-images  are  especially  con- 
nected with  the  sight-centre  Al. 

Further  Extension  of  Sight-centres.  —  Other  investigators 
have  thoroughly  traversed  the  ground  covered  by  the 
experiments  and  conclusions  of  Munk.  They  find  that  no 
blindness  of  the  clear  spot  of  vision  is  produced  in  the 
opposite  eye  by  extirpating  his  centre  Al,  in  the  case  of 
dogs.  It  is  even  claimed  that  the  most  extensive  lesion 
of  Munk's  entire  visual  area  does  not  necessarily  result  in 
the  loss  of  the  animal's  vision.  Moreover,  it  is  found  that 
disturbances  of  sight  may  follow  lesions  in  the  other  lobes, 
especially  in  the  frontal  lobes.  Some  years  since  it  was 
maintained  that  the  cuneus  is  especially  concerned,  with 
the  occipital  lobes,  in  the  functions  of  vision.  Regions 
adjacent  to  the  cuneus  are  also,  on  the  authority  of  some 
experimenters,  declared  to  be  connected  with  the  same 
functions. 

The  more  recent  experiments  with  stimulation  by  the 
electrical  current  seem  to  show  that  movements  of  the 
eyes  can  be  obtained  by  irritating  various  areas  in  and 
around  the  occipital  lobes.  Three  zones  are  mentioned  by 
one  authority  (Schafer) :  (1)  the  parts  about  the  parieto- 
occipital  fissure,  connected  with  movement  of  the  eyes 
downward;  (2)  the  lower  surface  of  the  lobe  and  of  the 
adjacent  convex  and  mesial  surfaces,  connected  with  move- 
ments of  the  eyes  upwards;  (3)  area  between  the  two, 
connected  with  lateral  movements. 

The  evidence  from  experiment  with  the  lower  animals 
does  not,  therefore,  clearly  and  definitely  indicate  where 
pathology  is  to  inquire  for  the  visual  areas  in  the  case  of 


SENSORY   AND   MOTOR   BKAIN   FUNCTIONS.  215 

man.  The  convex  surface  of  the  occipital  lobes  is  certainly 
indicated  in  a  general  way.  The  adjacent  convolutions 
on  the  same  lobe  and  in  the  cuneus,  etc.,  are  less  clearly 
indicated.  Indeed,  the  most  recent  investigations  (Lanne- 
grace,  1889)  on  dogs  and  monkeys  find  hemiopia  after 
injuries  in  almost  any  part  of  the  cortex,  and  ambliopia 
after  injuries  to  limited  areas  in  the  parietal  and  frontal 
lobes.  How  wide  and  somewhat  scattered  are  the  areas 
of  the  cortical  surfaces  which  are  more  or  less  definitely 
concerned  in  all  the  complex  phenomena  of  vision,  even 
among  the  highest  of  the  animals,  is  accordingly  apparent. 
How  much  more,  then,  may  we  expect  to  find  the  same 
complexity  of  phenomena,  and  variety  of  localities  in- 
volved, in  the  case  of  man  ! 

Exner  oil  Visual  Centres  in  Man.  —  The  answer  of  pathol- 
ogy to  the  question,  What  areas  of  the  human  cerebral 
cortex  are  chiefly  concerned  in  visual  sensations  and  per- 
ceptions? is  ambiguous.  The  method  of  "negative  cases," 
according  to  Exner,  yields  no  assured  results.  The  induc- 
tion does  not  point  out  any  "absolute  field"  of  vision. 
But  the  methods  of  "  percentage  "  and  of  "  positive  cases  " 
point  clearly  to  the  occipital  lobe,  and  especially  to  the 
upper  end  of  the  first  occipital  convolution  (Ol  in  the 
chart,  p.  205)  as  its  most  intensive  portion.  The  region 
of  less  intensity  extends  over  the  other  occipital  convolu- 
tions, the  cuneus,  and  the  adjacent  parts  of  the  lobulus 
quadratus. 

Additional  Evidence  from  Pathology.  —  An  increasing  num- 
ber of  positive  cases  indicate  that  the  induction  just  stated 
is  substantially  correct.  But  it  still  remains  true  that  we 
cannot  say  no  other  areas  than  those  mentioned  above  have 
particular  connection  with  the  phenomena  of  intelligent 
vision.  One  chief  authority  (Wilbrand)  has  been  led  to 
the  following  conclusions  respecting  what  he  calls  "  psychi- 
cal blindness."  If  the  impressions  be  cut  off  in  their 


216  PHYSIOLOGICAL   PSYCHOLOGY. 

course  along  the  optical  tract,  blindness,  in  the  more  ordi- 
nary sense  of  the  word,  results ;  but  visual  hallucinations, 
dream-visions,  and  subjective  light-sensations  are  still  pos- 
sible. If,  however,  the  perceptive  centre  (that  pointed  out 
by  Munk,  see  p.  199  f.)  be  destroyed  on  one  hemisphere,  then 
complete  cortical  blindness  takes  place  in  the  opposite  half 
of  the  field  of  vision.  If  this  centre  be  destroyed  in  both 
hemispheres,  subjective  visions,  hallucinations,  etc.,  are 
impossible.  If  the  visual  "memory-areas"  (see  p.  21 3 f.)  be 
also  thoroughly  destroyed,  then  all  impressions  of  form 
and  color  lose  their  psychical  and  intellectual  character. 
They  become  unmeaning  or  unfamiliar  impressions.  We 
cannot  vouch  for  the  full  accuracy  of  these  distinctions. 
They  await  further  confirmation. 

Kinds  of  "  Psychical  Blindness."  —  Disturbances  and  loss  of 
intelligent  and  appreciative  sight  may  be  due  to  a  variety 
of  causes,  occurring  either  singly  or  combined.  This  fact  is 
the  expression  of  the  variety  of  the  cortical  areas  that  are 
concerned  in  some  part  of  the  very  complex  activities  of 
such  vision  as  man  enjoys.  Thus,  to  adopt  provisionally 
the  classification  of  one  writer,  "  psychical  blindness  "  may 
be  due  (1)  to  disturbance  of  the  organism  for  associating 
the  perception  of  the  visual  object  with  other  ideas  (with- 
out disturbance  of  the  perception  itself) ;  or  (2)  to  dis- 
turbance of  both  the  perceptive  and  the  associative  activity ; 
or  (3)  to  disturbance  of  the  perception  exclusively.  Cor- 
responding to  these  necessary  factors  in  all  intelligent  and 
appreciative  vision  are  the  various  cortical  areas  and  tracts 
of  "  projection  "  and  "  association  "  fibres.  Thus  the  whole, 
apparatus  of  vision  involves  not  only  those  areas  which  have 
been  shown  to  be  especially  concerned,  but  also  other  less 
intensive  associated  areas  in  the  parietal,  temporal,  and 
even  frontal  lobes. 

Division  of  the  Visual  Field.  —  Persistent  and  skilful 
attempts  have  been  made  to  divide  the  general  field  of 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS.  217 

vision,  and  to  assign  to  the  divisions  distinct  sub-areas  in 
the  general  cortical  region  concerned  in  visual  perception. 
The  investigations  of  histology  seem  clearly  to  indicate 
that  in  the  higher  animals,  and  especially  in  man,  the  optic 
nerve  contains  one  system  of  fibres  which  crosses  over  to 
the  opposite  side  (either  in  the  optic  chiasm  or  beyond), 
and  one  system  which  remains  uncrossed.  The  retina  of 
each  eye  appears,  then,  in  man's  case,  to  be  represented  on 
the  cortical  surface  of  both  hemispheres  of  the  brain.  Patho- 
logical cases  confirm  this  conclusion  from  histology. 

The  assumed  state  of  the  case  is  then  described  by  one 
writer  in  the  following  terms :  "If  we  imagine  the  visual 
areas  of  the  two  cerebral  hemispheres  to  be  united  in  the 
middle  line,  we  may  conceive  each  retina  as  projected  in 
its  normal  position  over  the  united  area.  It  will  then  at 
once  appear  that  the  upper  and  lower  parts  of  both  retinas 
will  fall  upon  the  corresponding  parts  of  the  united  area ; 
that  the  outer  part  of  the  left  retina  and  the  inner  part  of 
the  right  will  fall  on  the  outer  portion  of  the  left  side  of 
the  united  area,  and  vice  versa  ;  and  that  a  vertical  line 
bisecting  each  retina  will  fall  along  the  line  of  union  of 
the  two  cerebral  areas." 

Cortical  Centres  of  Smell  and  Taste,  —  Nothing  definite  has 
yet  been  determined  as  to  those  areas  of  the  human  brain 
which  are  connected  with  sensations  and  perceptions  of 
smell  and  taste.  Both  centres  are  located  by  Dr.  Ferrier 
close  together  in  the  subiculum  (see  Fig.  68)  and  neigh- 
boring parts  of  the  convolutions  of  the  temporal  lobe. 
Munk,  however,  would  localize  smell  in  the  gyrus  hippo- 
campi. A  recent  writer  (Dr.  Mills),  while  admitting  that 
the  localization  of  the  cortical  centre  of  smell  is  still  un- 
certain, thinks  that  the  evidence  points  toward  the  region 
of  the  uncinate  convolution  and  its  vicinity. 

The  Centre  of  Hearing.  —  The  upper  convolution  in  the 
temporal  lobe  has  been  assigned  by  Dr*  Ferrier  to  the 


218  PHYSIOLOGICAL   PSYCHOLOGY. 

auditory  sensations.  But  this  auditory  centre  is  localized 
by  Munk  in  the  region  marked  B\  (see  Fig.,  p.  199),  for 
its  greatest  intensity;  and  with  less  intensity  in  the  ad- 
jacent regions  marked  B.  Recent  investigations  seem  to 
indicate  that  the  upper  temporal  convolution  can  be  com- 
pletely extirpated  without  disturbing  permanently  the 
sense  of  hearing.  With  considerable  probability  does  one 
authority  extend  the  so-called  "  auditory  sphere  "  over  the 
whole  surface  of  the  temporal  lobe,  and  probably  also  the 
"horn  of  Ammon." 

Centres  Concerned  in  Articulate  Speech.  —  To  speak  of  a 
cortical  centre  for  human  speech  seems  in  itself  to  involve 
an  absurdity.  All  the  processes  of  the  mind  are  deeply 
and  complexly  involved  in  the  use  of  language ;  if,  then, 
we  are  to  be  faithful  to  the  theory  of  localization  itself,  we 
are  compelled  to  admit  that  a  considerable  part  of  the 
entire  brain,  including  a  variety  of  centres  so-called,  must 
exercise  their  functions  in  connection  with  these  mental 
processes. 

In  treatises  of  the  years  1861-1865,  Broca  announced 
the  discovery  that  the  lower  convolution  of  the  frontal 
lobe  is  "the  seat  of  the  faculty  of  articulate  language." 
This  way  of  stating  the  case  involves  the  absurdity  to 
which  reference  has  just  been  made.  But  the  discovery 
in  physiology  thus  announced  was  of  the  highest  impor- 
tance and,  properly  stated,  has  maintained  its  place  among 
the  truths  of  cerebral  science. 

Phenomena  of  Aphasia,  —  Any  permanent  disturbance  or 
loss  of  the  power  to  apprehend,  or  to  express  one's  self  in, 
articulate  language,  if  it  is  due  to  lesions  of  the  cerebral 
cortex,  is  called  "  aphasia."  The  phenomena  of  this  dis- 
ease are  exceedingly  varied,  and  very  interesting.  They 
range  all  the  way  from  those  resembling  the  results  of 
inattention  in  normal  persons  (e.g.  such  as  that  of  the 
German  professor  who  certified  in  writing,  "A.  B.  has 


SENSOKY   AND   MOTOR   BKAIN   FUNCTIONS.  219 

attended  my  remarkable  lectures  in  chemistry  with  inor- 
ganic assiduity.")  to  the  utter  loss  of  intelligent  speech, 
in  cases  of  progressive  paralysis  with  dementia. 

Sometimes  the  aphasic  patient  is  entirely  speechless,  but 
understands  what  is  said  to  him,  and  can  express  himself 
in  writing.  Sometimes  he  can  pronounce  words  of  one 
syllable  only  ;  sometimes  only  a  few  senseless  or  extraor- 
dinary syllables  or  words.  Not  infrequently  the  ability  to 
render  certain  words  or  sounds  is  joined  with  the  inability 
to  render  other  closely  similar  words  or  sounds,  in  a  most 
surprising  way.  One  patient,  thus  afflicted,  could  say 
"  Bon  jour,"  but  could  not  say  "  bonbon."  In  another 
celebrated  case  the  entire  vocabulary  of  the  aphasic  person 
was  limited  to  the  five  words,  oui,  non,  tois  (for  trois), 
toujours,  and  Le  Lo  (instead  of  Le  Long,  the  man's  name). 
Four  of  these  words  were  used  with  a  substantially  correct 
meaning ;  but  "  toujours  "  was  the  word  employed  when- 
ever the  patient  could  not  express  his  meaning  by  gestures 
or  by  the  rest  of  his  stock  of  words. 

Kinds  of  Aphasia.  —  The  variety  of  phenomena  connected 
with  this  form  of  cerebral  disease  is  such  as  to  provoke 
investigators  to  a  more  careful  classification  of  the  cases. 
Thus  various  subdivisions  have  been  made.  The  word 
agraphia  has  been  employed  for  the  inability  to  express 
thought  in  written  language,  —  an  inability  which  may  be 
incomplete  or  absolute.  In  some  cases,  highly  cultivated 
persons  become  unable  to  produce  a  single  letter  with  the 
pen.  Others  write  long  rows  of  letters  arranged  in  mean- 
ingless fashion,  or  with  a  genuine  word  occurring  here 
and  there. 

In  certain  cases  of  aphasia  it  is  "  word-deafness  "  which 
is  the  prominent  factor  in  the  disease.  Persons  thus  af- 
jlicted  hear  words  as  confused  murmurings,  with  no  mean- 
ing in  them ;  at  the  same  time  the  sense  of  hearing  for  the 
tick  of  a  watch  may  be  very  acute.  In  other  cases,  the 


220  PHYSIOLOGICAL   PSYCHOLOGY. 

patient  can  hear  and  articulate,  but  the  "  acoustic  image '.' 
of  the  word  as  a  symbol  of  the  idea  has  perished. 

In  many  cases  of  aphasia  the  phenomenon  of  what  is 
called  "  word-blindness "  is  the  most  prominent  factor. 
The  connection  of  this  disease  with  disturbances  of  the 
visual  centres  has  been  noticed  by  many  observers.  Some 
have  held  that  "  optical  aphasia  "  is  a  distinct  kind.  Of 
seven  reported  cases  of  cerebral  defect  of  vision,  five  of 
which  had  "  psychical  blindness  "  and  could  not  read,  six 
cases  showed  extensive  lesions,  generally  in  the  occipital 
and  teinporo-occipital  regions.  Hence  we  may  argue  that 
the  sight-centres  in  the  occipital  lobes  are  connected  by 
association-fibres  with  the  centres  for  uttering  language  in 
the  temporal  and  frontal  lobes. 

Novel  affections  have  also  been  noticed  in  which  the 
patients  can  read  a  few  lines,  but  apparently  get  no  sense 
from  it,  and  give  up  the  attempt  in  despair.  The  name  of 
"  dyslexia  "  has  been  given  to  such  cases ;  and  in  some  of 
them  post-mortem  examination  has  shown  lesions  interfer- 
ing with  the  tracts  between  the  visual  areas  and  the  con- 
volution in  which  Broca  located  articulate  speech. 

Dr.  Starr  suggests  a  name  ("  apraxia  ")  for  a  wider  class 
of  cases,  of  which  "  word-deafness  "  and  "  word-blindness  " 
are  the  best  known  examples.  The  significant  feature  of 
such  cases  is  the  inability  to  recognize  the  use  or  import  of 
an  object.  Of  this  inability  there  may  be  as  many  kinds 
as  there  are  kinds  of  sensations.  The  cerebral  disease  con- 
sists in  the  lesion  of  the  connections  which  are  normally 
maintained  among  the  "  residua "  of  the  various  groups  of 
sense-impressions . 

Cerebral  Areas  of  Lesion  in  Aphasia.  —  In  Exner's  collec- 
tion of  cases,  all  but  one  of  the  31  lesions  resulting  in 
aphasia  were  on  the  left  hemisphere  of  the  brain.  Dr. 
Seguin,  out  of  260  cases,  calculated  the  proportion  of 
aphasias  due  to  lesion  on  the  left  side  as  compared  with 


f 

SENSORY   AND   MOTOR   BRAIN    FUNCTIONS.  221 

the  right,  to  be  as  243 : 17  or  14.8 : 1.  It  appears  then 
that,  so  far  at  least  as  the  motor  functions  are  con- 
cerned,^ speech  is  left-brained.  In  this  (the  left)  hemi- 
sphere, the  anterior  central  convolution  and  the  adjacent 
convolutions  of  the  frontal  lobe,  but  especially  the  back 
part  of  the  lower  frontal  convolution,  have  much  the  high- 
est intensity  as  seats  of  aphasic  lesions.  Of  53  cases  care- 
fully collected  by  one  authority,  50  were  in  the  left  hemi- 
sphere, 24  in  the  lower  frontal  convolution,  34  in  this 
convolution  and  adjacent  parts,  19  either  in  the  Island  of 
Reil  alone  or  in  it  and  adjacent  parts.  Yet  the  same 
authority  gives  2  cases  of  aphasia  following  lesions  in  the 
front  part  of  the  frontal  lobe,  3  in  the  parietal,  4  in  the 
occipital. 

Further  Distinctions  in  Areas  of  Speech.  —  Attempts  have 
been  made,  Avith  more  or  less  of  probability,  to  localize 
the  lesions  which  occasion  the  different  kinds,  or  are 
connected  with  the  different  factors  and  phases,  of  aphasia. 
Thus  Exner  is  inclined  to  assign  "  motor  aphasia  "  to  the 
third  frontal  convolution,  "  word-deafness  "  to  the  middle 
temporal  convolution,  and  "agraphia"  to  the  lower  and 
front  part  of  the  parietal  lobe.  In  partial  but  substantial 
agreement  with  him,  another  authority  would  locate  "  hear- 
ing language  "  in  the  first  and  part  of  the  middle  temporal 
convolutions ;  "  seeing  words  "  in  the  lower  parietal ; 
"  writing "  at  the  foot  of  the  left  middle  frontal ;  and 
"  speaking  words  "  at  the  foot  of  the  left  lower  frontal 
convolution.  Each  centre  is  thus  situated  amidst  larger 
related  areas,  — the  motor,  in  the  wider  field  of  arm,  tongue, 
and  jaw ;  and  the  sensory,  in  the  general  fields  of  hearing 
and  sight.  Each  centre  is,  therefore,  the  focus  of  certain 
kinds  of  memory-images. 

The  foregoing  delineations  are  rather  more  definite  than 
it  is  wise  at  present  to  attempt  to  be.  We  cannot  do  better 
than  to  close  this  branch  of  the  discussion  with  the  remark 


222  PHYSIOLOGICAL   PSYCHOLOGY. 

of  Kussmaul,  "It  is,  a  priori,  probable  that  an  enormous 
association  tract  in  the  cortex  has  been  assigned  to  speech, 
even  though  the  key-board  of  sound  may  be  confined  to 
the  anterior  cortical  regions."  With  reference  to  the  last 
clause,  however,  it  is  to  be  noticed  that  the  loss  of  power 
to  sing  and  to  understand  melodies,  or  to  use  and  under- 
stand numbers,  is  not  necessarily  connected  with  the  loss 
of  articulate  speech. 

Evidence  from  Histology  and  Anatomy.  —  The  general  dis- 
tribution of  motor  and  sensory  areas  which  has  been  made 
above  is  confirmed  —  or  at  least  it  is  not  disturbed  —  by 
researches  in  comparative  histology  and  anatomy.  That 
the  motor  tracts  from  below  run  to  the  frontal  and  front 
parietal  and  temporal  regions  of  the  brain,  while  the  sen- 
sory lie,  on  the  whole,  in  the  direction  toward  the  hinder 
cerebral  parts,  can  scarcely  be  doubted  (compare  p.  72  f.). 
It  is  perhaps  more  doubtful,  and  yet,  on  the  whole,  prob- 
able —  as  says  Dr.  Starr  —  that  "  the  third  set  of  fibres  of 
the  projection  system  includes  those  which  lie  just  posterior 
to  the  motor  tract,  and  fill  up  to  a  considerable  extent  the 
space  between  it  and  the  radiation  of  the  visual  tract, 
towards  the  occipital  lobe."  This  set  of  fibres,  he  thinks, 
convey  the  sensory  impulses  of  touch,  pain,  temperature, 
and  the  muscular  sense.  They  lie  around,  and  to  a  certain 
extent  coincide  with,  and  interpenetrate,  the  motor  areas. 

RELATION      OF      THE      CEREBRAL     AREAS      TO    "GENERAL 
INTELLIGENCE." 

The  more  ardent  advocates  of  the  theory  of  the  local- 
ization of  cerebral  functions  find  it  difficult  to  refrain  from 
assigning  some  portion  of  the  cerebral  cortex  to  the  for- 
mation of  concepts,  and  to  the  mental  activities  sometimes 
spoken  of  as  "general  intelligence."  Of  course,  for  this 
purpose  the  frontal  regions  offer  themselves  as  peculiarly 
tempting.  General  considerations  of  comparative  anatomy 


SENSORY  AND  MOTOR   BRAIN   FUNCTIONS.  223 

might  be  said  to  favor  this  view.  For  it  is  with  respect  to 
the  development  of  these  regions,  as  one  most  significant 
feature,  that  the  human  brain  surpasses  that  of  all  the 
other  animals.  Experimental  evidence  might  also  be 
appealed  to, — such  as  that  which  finds  the  mentality  of 
birds,  for  example,  whose  fore-brains  have  been  removed 
without  injury  to  remaining  portions,  reduced  to  a  con- 
dition resembling  idiocy. 

On  the  other  hand,  there  are  perhaps  no  other  portions 
of  the  human  brain  where  so  extensive  lesions  may  occur 
with  little  or  no  impairment  of  any  bodily  or  mental  func- 
tions, as  the  frontal  regions.  Small  lesions  in  other  regions 
are  not  infrequently  productive  of  much  more  serious 
mental  disturbance. 

It  should  also  be  noticed  that  the  words  "  general  intel- 
ligence "  are  somewhat  ambiguous,  and  may  be  really 
misleading.  Strictly  speaking,  there  is  no  such  thing  as 
general  intelligence.  Especially  in  the  earlier  stages  of 
development,  and  with  the  lower  animals,  any  impairment 
of  the  sensory  or  motor  functions  occasions  a  certain  dis- 
turbance or  loss  of  "  intelligence."  In  a  case  like  that  of 
aphasia,  in  man,  how  shall  we  separate  between  the  def- 
inite and  concrete  loss  of  functions  which  we  designate  by 
"psychical  deafness,"  or  "psychical  blindness,"  and  the 
disturbance  and  loss  of  general  mental  power?  All  intel- 
ligence is  intelligence  about  something  or  other,  and  resting 
upon  a  basis  of  sensations  and  volitions. 

Moreover,  the  phenomena  to  which  the  veteran  opponent 
(Goltz)  of  the  theory  of  localization  constantly  appeals, 
show  that,  in  the  lower  animals,  the  descent  toward  idiocy 
is,  in  a  general  way,  proportioned  to  the  amount  of  cere- 
bral substance  which  has  been  functionally  disturbed  or 
extirpated.  Even  temporary  functional  impairment  of  the 
cerebral  centres  tends  to  pull  any  one  down  toward  idiocy. 
Such  impairment  occasions  a  diminution  of  mental  vigor 


224  PHYSIOLOGICAL  PSYCHOLOGY. 

which  shows  itself  in  more  or  less  specific  ways,  according 
to  circumstances.  Goltz  describes  a  dog  which  lived  for 
fifteen  months  after  having  lost  one  entire  hemisphere, 
basal  ganglia  included.  Both  motion  and  sensibility  were 
impaired  on  the  side  opposite  the  lesion  ;  but  there  was 
complete  loss  of  no  sensory  or  motor  function.  The 
animal  was  a  simpleton,  without  fear  or  sportiveness,  and 
with  impaired  hearing  and  sight.  But  the  removal  of  one 
frontal  lobe  from  an  animal  is  found  to  occasion  little  or 
no  severe  disturbance  of  mental  functions.  With  both 
frontal  lobes  gone,  however,  the  animal  cannot  eat  unaided, 
nor  use  his  paws  as  hands.  The  removal  of  the  occipital 
lobes  occasions,  Goltz  believes,  far  more  profound  changes 
than  loss  of  both  eyes ;  the  animal  then  loses  psychical  fear 
and  interest,  and  is  mentally  degenerate. 

In  man's  case  we  can  localize  with  considerable  success 
the  functions  on  which  the  psychical  quality  of  sensory 
impressions  is  dependent;  and  we  can  point  out  the  tracts 
which  must  be  traversed  if  memory-images  are  to  be 
aroused,  and  the  impressions  attain  a  meaning  and  connec- 
tion with  the  past  mental  life.  But  as  to  cortical  areas 
which  may  serve  as  a  physical  basis  for  the  mental  activi- 
ties that  are  "  logical  "  or  "  intellectual,"  —  in  the  higher 
sense  of  these  words,  —  we  are  quite  in  the  dark  as  to 
where  to  look  for  them,  or  as  to  the  use  to  which  we  should 
put  them  in  case  they  could  be  found. 

Summary  of  Principles.  —  Three  principles  seem  to  sum 
up  the  results  obtained  by  discussion  of  the  evidence  ad- 
duced in  the  two  preceding  chapters. 

1.  The  Principle  of  Use  and  the  Law  of  Habit.  The 
different  elementary  parts  of  the  nervous  system  become 
capable  of  performing  their  specific  functions,  only  when 
brought  into  proper  connections  and  exercised  in  the 
performance  of  those  functions.  No  elements  or  groups  of 


SENSORY   AND   MOTOR   BRAIN   FUNCTIONS.  225 

elements  act  in  isolation ;  what  they  do,  and  can  do, 
depends  upon  their  connection  with  other  elements.  This 
is  especially  true  of  the  different  minuter  or  larger  areas 
of  the  cerebral  cortex.  Their  functions  are  dependent 
upon  their  relations  to  one  another  and  to  the  inferior 
regions  of  the  brain,  as  joined  together  by  "  association- 
fibres  "  and  "  projection-fibres." 

Moreover,  the  repeated  action  of  the  nervous  elements, 
in  the  connections  in  which  they  are  placed,  develops  in 
them  a  special  fitness  for  performing  specific  functions. 
The  areas  of  the  cortex  improve  by  exercise.  By  repeated 
activity,  in  their  appropriate  connections,  they  gain  in 
facility  and  value  with  respect  to  their  specific  functions. 

2.  The  Principle  of  a  Local  Specialization  of  Function. 
In  the  cerebral  cortex,  as  elsewhere  through  the  entire 
nervous  system,  certain  parts  have,  in  all  normal  and 
ordinary  circumstances,  certain  specific  functions  to  per- 
form. In  the  spinal  cord  we  found  particular  areas,  either 
as  located  by  a  cross-section  at  each  altitude,  or  as  so-called 
"  centres  "  placed  above  and  below  each  other  in  the  length 
of  the  cord,  to  have  specific  functions  assigned  to  them. 
In  the  lower  parts  of  the  brain  the  principle  of  the  local- 
ization of  function  appears  to  be  also  carried  out.  The 
evidence  adduced  in  the  last  two  chapters  establishes 
beyond  reasonable  doubt  the  existence  of  the  same  prin- 
ciple as  applied  to  different  parts  of  the  cortex  of  man's 
brain.  And,  indeed,  it  is  just  here  that  we  should  expect 
to  find  the  most  definite  and  perfect  application  of  the 
principle. 

So-called  "  centres,"  or  "  areas,"  or  "  fields,"  of  the  sur- 
face of  man's  brain  are  in  no  case,  however,  to  be  regarded 
as  portions  of  its  nervous  substance  that  mark  the  limits 
within  which  specific  functions  are  always  rigidly  confined. 
Such  "  centres  "  are  not  to  be  thought  of  as  mathematical 


226  PHYSIOLOGICAL   PSYCHOLOGY. 

points  or  as  definitely  circumscribed  collections  of  cells. 
They  do  not  appear  to  be  perfectly  isolated  localities. 
They  are  not  necessarily  the  same  in  their  exact  outlines 
for  individuals  of  the  same  species,  or  for  the  same  indi- 
vidual at  all  times.  They  widen  when  a  heightened  energy 
is  demanded  of  them.  They  obviously  overlap  and  inter- 
penetrate in  certain  cases.  Especially  is  this  true  of  the 
regions  in  which  the  motor  and  sensory  functions  are  con- 
nected for  the  control  of  the  same  parts  of  the  body. 
They  are  intimately  interconnected  and  associated  in 
function ;  so  that  one  of  them  cannot,  as  a  rule,  be  cut  out 
without  injury  to  others ;  or  its  function  greatly  impaired 
without  disturbing  the  function  of  other  associated  cen- 
tres. 

3.  The  Principle  of  Substitution.  Furthermore,  the 
performance  of  the  functions  allotted,  as  it  were,  to  these 
so-called  centres,  is  not  necessarily,  under  all  circum- 
stances, confined  to  them.  If  such  areas  become  absolutely 
or  relatively  unfitted  to  perform  their  normal  functions,  it 
is  possible,  within  certain  limitations,  for  other  areas  to 
assume  these  functions.  The  areas,  however,  which  can 
be  substituted  must  have  the  proper  connections.  It  is 
due,  in  large  part,  to 'the  working  of  this  principle  of  sub- 
stitution, that  animals  subjected  to  experiments  in  extirpa- 
tion, as  a  rule,  recover  the  powers  of  sensation  and  motion 
which  they  have  temporarily  lost.  A  certain  large  elas- 
ticity, as  it  were,  of  the  nervous  system  is  implied  in  the 
very  laws  of  reflex  or  sensory-motor  activity  as  applied  to 
the  spinal  cord  (see  p.  139  f.).  This  principle  does  not 
operate  arbitrarily ;  it  will  not  meet  all  possible  demands 
made  upon  it. 

The  portions  of  the  same  hemisphere  of  the  brain  that 
are  just  adjacent  to  the  so-called  "  centres  "  (the  larger 
areas  surrounding  or  continuous  to  the  smaller),  and,  on 
account  of  its  bilateral  structure,  the  corresponding  por- 


SENSORY  AND   MOTOR   BRALN   FUNCTIONS.  227 

tions  of  the  other  hemisphere,  are  best  capable  of  exercising 
their  substitutive  functions.  The  assumed  functions  also 
fall,  of  course,  under  the  law  of  habit.  Perhaps  these 
statements  cover  all  that  it  will  finally  be  found  necessary 
to  admit. 


CHAPTER  X. 

THE   QUALITY  OF  SENSATIONS. 

THE  variety  of  our  sensations  seems,  on  first  reflection, 
bewilderingly  great.  But  the  popular  way  of  viewing 
them  has  reduced  them  all  to  five  classes,  according  to  the 
organs  of  the  body  through  which  the  sensations  are  known 
to  be  received.  Hence  the  five  kinds  of  senses  —  smell, 
taste,  hearing,  sight,  and  touch  —  which  everybody  recog- 
nizes. The  inadequacy  and,  in  some  respects,  inaccuracy 
of  this  popular  classification  are  readily  made  apparent. 
But  it  is  not  seen,  without  careful  and  detailed  scientific 
research,  what  classification  ought  to  take  its  place.  The 
various  and  uncertain  uses  of  the  word  "feeling  "  are  cal- 
culated to  emphasize  our  doubts  and  difficulties  on  this 
point. 

Simple  Sensations.  —  Strictly  speaking,  there  are  no  ex- 
periences of  which  we  are  conscious  that  can  be  called 
simple  —  or  absolutely  uncompounded  —  sensations.  In- 
deed, in  all  our  adult  life  we  have  no  experience  even  of 
pure  but  complex  sensations,  as  such,  —  that  is,  of  sensa- 
tions regarded  as  states  of  consciousness  disconnected  from 
images  of  memory  and  imagination,  and  unrelated  to 
things,  perceived  or  imagined,  as  their  so-called  "quali- 
ties." Moreover,  the  simplest  sensation  which  we  can 
detect  in  connection  with  our  perceptions  or  memories  of 
things  is  no  more  absolutely  simple  to  psychology,  in  its 
nature,  than  is  the  drop  of  water  to  chemistry. 

The  "  simple  sensation  "  is  then  a  fiction  of  psycho-physi- 
cal science.  It  is  not  realizable  as  a  state  of  consciousness 

228 


QUALITY   OF   SENSATIONS.  229 

in  experience.  It  is  a  theoretical  factor  into  which  science 
breaks  up  those  complexes  of  consciousness  which  have 
the  predominating  characteristics  of  all  sense-experience. 

Quality  distinguished  from  Quantity.  —  Consciousness  en- 
ables us  to  distinguish  between  the  quality  and  the  quan- 
tity, or  intensity,  of  our  sensations.  We  are  immediately 
aware  both  of  the  kind  of  the  mental  affection  which  arises 
through  excitation  of  the  organs  of  sense,  and  also  of 
variations  in  its  amount.  Thus  a  distinction  is  possible 
between  "  the  how  "  and  the  "  how  much  "  of  the  resulting 
state.  That  the  quality  and  the  quantity  of  sensations 
are  closely  related,  our  experience  makes  perfectly  clear. 
Intense  smells  and  tastes  are  different  from  weak  ones,  in 
their  characteristic  quality,  even  when  they  are  excited  by 
the  same  object.  Very  intense  sensations  of  every  kind 
tend  to  pass  over  into  sensations  of  pain.  Sensations  of 
light  touch  differ  in  kind  from  those  produced  by  heavier 
pressure  of  the  same  object  on  the  same  locality  of  the 
organ.  Yet  the  distinction  between  quality  and  quantity 
is  clearly  made  by  the  consciousness  of  every  one. 

Questions  relating  to  the  Determination  of  Quality.  —  The 
inquiries  which  physiological  psychology  raises  concerning 
the  quality  of  sensation  are,  chiefly,  these  four :  (1)  What 
is  the  precise  locality  of  the  organism  where  the  specific 
excitation  which  occasions  each  kind  of  sensation  origi- 
nates? (2)  What  is  the  character  of  the  stimulus,  and 
the  nature  of  its  action  upon  the  organism,  in  producing 
the  specific  excitation  ?  (3)  What  are  the  various  kinds 
of  sensations  which  appear  in  consciousness  and  the  various 
corresponding  kinds  of  stimuli  on  which  the  sensations 
are  dependent?  (4)  What  are  the  laws  by  which  the 
quality  of  the  sensations  is  related  to  the  several  kinds  of 
stimuli?  None  of  these  questions  can  be  answered  com- 
pletely by  modern  experimental  psychology.  But  some- 
thing of  a  strictly  scientific  character  can  be  said  in  reply 


230  PHYSIOLOGICAL  PSYCHOLOGY. 

to  each;  and  none  of  them  can  be  properly  neglected 
in  our  considerations.  We  shall  not,  however,  think  it 
necessary  always  to  keep  their  consideration  separate. 

SENSATIONS   OF   SMELL  AND    TASTE    QUALITATIVELY 
CONSIDERED. 

In  beginning  with  these  sensations  we  are  considering 
those,  first,  which  are  least  intellectual  in  quality,  and  at 
the  same  time  most  indefinite  and  difficult  to  reduce  to 
terms  of  scientific  statement. 

Excitable  Region  for  Sensations  of  Smell.  —  It  has  already 
been  shown  (p.  74  f .)  that  the  part  of  the  mucous  membrane 
of  the  nasal  passages  known  as  the  regio  olfactoria  contains 
the  end-organs  of  smell.  Here  the  nerve  of  smell  (olfac- 
torius)  is  spread  out.  It  must  be  reached  by  the  stimulus 
being,  in  all  ordinary  circumstances  at  least,  borne  thither 
by  the  current  of  air  in  the  act  (usually,  if  not  always)  of 
inspiration. 

Stimulus  of  Sensations  of  Smell.  —  The  excitation  of  the 
end-organs  of  this  sense  seems  to  require  that  the  stimulus 
should  act  upon  them  in  gaseous  form.  Thus  objects  like 
arsenic,  which  at  ordinary  temperatures  are  inodorous, 
when  vaporized  by  heat,  excite  intense  sensations  of  smell. 
Fluid  bodies  which  give  off  an  odorous  reek,  when  brought 
in  their  fluid  form  into  contact  with  the  organs,  as  a  rule, 
have  no  smell.  Most  observers  have  followed  the  opinion 
of  Weber,  who  held  that  no  fluid,  not  even  eau  de  cologne, 
when  poured  into  the  nostrils  and  remaining  against  the 
organs,  can  excite  olfactory  sensations.  The  reason  for 
this  has  been  attributed  to  the  temporary  impairment  of 
the  organs  by  being  soaked,  or  to  the  mechanical  barrier 
which  the  fluid  makes  between  the  odorous  particles  and 
the  apparatus  of  smell. 

The  conclusion  of  Weber  has  more  recently  been  con- 
tested. It  has  been  considered  that  fish  have  true  sensa- 


QUALITY  OF   SENSATIONS.  231 

tions  of  smell.  And  some  observers  report  that,  by  using 
a  _L  tube  and  introducing  into  the  nostrils  solutions  of 
camphor,  clove  oil,  cologne,  etc.,  they  have  succeeded  in 
exciting  the  specific  smells  of  these  substances. 

Mechanical  and  Electrical  Excitation  of  Smell.  —  Some 
physiologists  have  a'sserted  that  they  could  obtain  sensa- 
tions of  smell  by  different  forms  of  mechanical  irritation, 
such  as  vibration  of  the  nostrils,  violent  sneezing,  etc. 
Nearly  a  century  ago  Ritter  experimented  by  using  bits  of 
graphite  and  zinc  thrust  into  the  nostrils,  and  thought  he 
thus  excited  genuine  sensations  of  smell.  He  described 
the  positive  pole  as  effecting  a  trace  of  smell  like  that  of 
"  ammonia  "  ;  the  negative  pole  produced  a  kind  of  "  sour  " 
smell.  It  is  by  no  means  certain  that  these  sensations 
were  not  sensations  of  touch  and  taste  rather  than  specific 
sensations  of  smell.  And  although  some  modern  experi- 
menters claim  to  have  a  distinct  sense  of  smell,  for  ex- 
ample, with  the  cathode  in  the  nose  on  opening  the 
current,  and  with  the  anode  on  making  the  current,  the 
electrical  stimulation  of  specific  sensations  of  this  sense 
can  scarcely  be  said  to  be  experimentally  established. 
There  is  no  proof  that  thermic  stimulation  will  excite  the 
sense  of  smell. 

Subjective  Sensations  of  Smell.  —  Experiments  to  prove 
that  the  sense  of  smell  may  be  excited  in  animals  by 
injecting  odorous  substances  into  their  veins  are  very 
uncertain.  Human  pathological  cases  show  that  com- 
pression of  the  olfactory  nerve  by  tumors  may  produce 
sensations.  There  is  no  doubt  that  disturbances  of  the 
central  organs,  such  as  accompany  insanity,  may  cause 
subjective  smells.  Indeed,  to  be  thus  afflicted  is  some- 
times symptomatic  of  disease  of  the  brain.  And  we  know 
how  powerfully  the  brains  of  some  persons  are  affected,  so 
that  nausea  and  giddiness  result,  by  even  very  weak  odors 
from  some  substances. 


232  PHYSIOLOGICAL  PSYCHOLOGY. 

Properties  of  Odorous  Bodies.  —  There  seems  to  be  no  one 
characteristic  which  a  body  must  possess  in  order  to  excite 
the  specific  kind  of  sensation  which  we  distinguish  as  that 
of  smell.  Some  plants  are  odorous  by  day  alone,  others  by 
night  alone.  Some  have  a  smell  when  dry;  others  give 
off  only  a  weak  odor  when  dry,  but  a  stronger  one  when 
moistened.  In  general,  the  effect  of  any  odorous  sub- 
stance depends  upon  the  ease  with  which  it  may  be  vapor- 
ized, and  the  speed  and  extent  of  its  diffusion  through  the 
atmosphere. 

In  1756  it  was  discovered  (by  Romieu)  that  small  bits 
of  camphor  on  water  exhibit  a  peculiar  rotary  motion.  It 
was  afterwards  shown  that  other  odorous  bodies  have  a 
similar  motion  on  the  surface  of  water;  and  that  a  thin 
layer  of  water  on  a  perfectly  clean  plate  will  withdraw 
itself  as  soon  as  pulverized  camphor  is  spread  upon  it. 
Similar  phenomena  have  been  noticed  in  the  cases  of  some 
two  hundred  odorous  substances  of  either  vegetable  or 
animal  structure.  From  such  data  the  conclusion  is  drawn 
that  all  odorous  substances  have  the  power,  especially  when 
in  contact  with  moisture,  to  set  up  such  a  motion  of  their 
outside  particles  as  distributes  them  through  the  surround- 
ing atmosphere.  Beyond  the  general  theory,  that  the 
power  to  give  off  those  peculiar  "  effluvia  "  which  excite 
the  end-organs  of  the  olfactory  nerve  is  characteristic  of 
all  odorous  bodies,  it  cannot  be  said  that  much  is  known. 

Classification  of  Smells.  —  The  specific  sensation  of  smell 
must,  first  of  all,  be  distinguished  from  other  forms  of  sen- 
sation with  which  it  is  combined  and  ordinarily  confounded. 
Many  so-called  sensations  of  taste  (as  that  of  the  onion, 
etc.)  are  really  sensations  of  smell.  Substances  like  am- 
monia and  acetic  acid  excite  sensations  of  so-called  "  com- 
mon feeling"  through  their  action  on  the  trigeminus  as 
well  as  the  olfactory  nerve. 

But   after   these    distinctions    are    carefully   made,   all 


QUALITY   OF   SENSATIONS.  233 

attempts  to  classify  sensations  of  smell,  as  such,  remain 
unavailing.  The  division  into  pleasant  and  unpleasant 
depends  upon  the  changing  whims  of  individuals.  To 
some  persons  the  smell  of  assafoetida,  of  burning  feathers, 
of  rank  cheese,  is  pleasant.  A  classification  according  to 
the  objects  which  yield  the  odor  ("smell  of  a  rose,"  etc.) 
is  not  a  classification  of  sensations  of  smell  at  all.  A  clas- 
sification on  chemical  grounds  is  unsatisfactory ;  chemists 
differ  much  concerning  the  smell  of  the  same  substances. 
Nor  have  the  attempts  to  distinguish  various  olfactory 
fibres,  or  systems  of  fibres,  as  appropriated  to  specific  sen- 
sations, been  successful. 

We  are  obliged  then  to  say  that  no  known  principle  will 
bring  order  out  of  this  bewildering  confusion.  There  is 
no  classification  of  the  sensations  of  smell,  as  such.  To 
quote  from  a  prominent  authority  :  Sensations  of  smell 
form  "a  discrete  manifoldness  which  has  an  unknown 
arrangement." 

Our  knowledge  respecting  /Sensations  of  Taste  and  their 
excitement  and  laws  is  only  a  little  more  advanced  than 
that  respecting  sensations  of  smell. 

Excitable  Regions  for  Sensations  of  Taste.  —  The  question 
whether  a  tastable  substance  excites  specifically  the  same 
sensations,  when  applied  to  all  places  of  the  organ  of  taste, 
is  somewhat  difficult  to  answer  experimentally.  Descrip- 
tions which  speak  of  tastes  as  "prickly,"  "piquant,"  "cool- 
ing," etc.,  confound  other  sensations  with  those  of  this 
sense.  The  more  general  conclusion  seems  to  be,  that 
sweet  and  sour  are  tasted  chiefly  with  the  tip  of  the  tongue, 
bitter  and  alkaline  with  its  roots.  In  1888,  in  the  laboratory 
of  Johns  Hopkins,  it  was  discovered  that  a  certain  deriva- 
tive of  saccharine  would  produce  sensations  of  bitter  when 
applied  to  the  back  part  of  the  tongue,  and  of  sweet  when 
applied  to  the  tip  and  borders  of  the  anterior  half.  It 
should  be  said,  however,  that  another  observer  reports  the 


234  PHYSIOLOGICAL   PSYCHOLOGY. 

sensibility  of  the  root  of  the  tongue  for  sweet  greatest  in 
nine  cases  out  of  ten,  with  which  he  experimented,  and  of 
the  edges  of  the  tongue  for  sour,  in  seven  cases  out  of  ten. 
The  same  observer,  however,  found  that  the  root  retains 
best  its  taste  for  bitter,  and  worst  its  taste  for  sour. 

In  all  such  experiments  considerable  allowance  must  be 
made  for  the  idiosyncrasies  of  individuals.  It  must  also  be 
remembered  that  it  is  difficult  carefully  to  circumscribe  the 
application  of  stimulus  to  the  end-organs  of  taste.  More- 
over, in  some  cases  the  sensibility  to  excitement  extends 
outside  of  the  tongue  more  widely  than  is  common ;  it 
may  be  found  in  the  soft  palate  and  the  contiguous  arch. 
Indeed,  the  record  of  one  patient  is  given  who,  when  the 
entire  tongue  had  been  removed,  retained  some  taste 
caused  by  touching  the  back  of  the  throat  or  the  mucous 
membrane  of  the  stump. 

Stimulus  of  Sensations  of  Taste,  —  Only  fluid  bodies,  or 
such  as  are  soluble  in  a  fluid  or  menstruum,  excite  sensa- 
tions of  taste.  Absolutely  insoluble  bodies  are,  without 
exception,  tasteless.  Not  all  soluble  substances,  however, 
excite  sensations  of  taste  ;  and  no  known  law  regulates  the 
relation  between  the  two.  It  has  been  claimed  by  some 
experimenters  that  certain  gases,  when  made  to  act  upon 
the  organs  of  taste,  excite  in  them  the  specific  sensations 
of  this  sense.  It  is  difficult,  however,  to  prove  that  the 
tongue  has  been  so  thoroughly  dried  in  any  case,  as  to 
prevent  the  absorption  of  these  gases  by  its  moist  capillary 
layer. 

Mechanical  and  Electrical  Excitation  of  Taste.  —  It  is  doubt- 
ful whether  the  sensation  of  taste  can  be  excited  by 
mechanical  means.  Certain  authorities  of  high  rank  de- 
scribe such  sensations  as  mingled  with  the  feelings  that 
follow  rubbing  or  pressing  the  tongue.  The  debate  over 
the  question  whether  electrical  stimulation  excites  sensa- 
tions of  this  sense  continued  for  a  hundred  years.  It  was 


QUALITY  OF   SENSATIONS.  235 

finally  shown  that,  when  a  chain  of  four  persons  is  arranged 
in  such  a  manner  as  to  send  a  current  of  electricity  through 
the  tongue  of  one,  the  eyeball  of  another,  and  the  muscles 
of  a  frog-preparation,  held  by  two  of  the  four,  the  same 
excitation  causes,  simultaneously,  an  acid  taste  in  the 
mouth  of  one  observer,  a  flash  of  light  in  the  eye  of 
another  observer,  and  a  movement  of  the  muscles  of  the 
frog.  Other  experiments  confirm  the  view  that  electricity 
is  an  excitant  of  the  sensations  of  taste. 

Subjective  Sensations  of  Taste.  —  The  attempts  made  to 
prove  that  animals  may  t>e  affected  with  sensations  of  this 
sense  by  injecting  tastable  substances  into  their  blood, 
have  led  to  no  result.  Most  of  the  alleged  instances  of 
subjective  sensations  of  taste  are  probably  due  to  substances 
really  brought  to  the  tongue  in  the  saliva.  It  is  note- 
worthy that  we  rarely  or  never  dream  in  terms  of  this  sense. 

Properties  of  Tastable  Substances.  —  As  to  what  it  is  in 
certain  substances  which  fits  them  to  excite  the  end-organs 
of  the  tongue  and  soft  palate,  we  are  much  in  the  dark. 
Experiments  lie  in  the  line  of  discovering  some  relation 
between  the  chemical  constitution  and  action  of  these  sub- 
stances and  the  different  kinds  of  taste.  This  relation  has 
been  thought  to  be  of  the  simplest  sort  with  the  acids ;  a 
great  variety  of  which,  when  we  exclude  the  sense  of  smell, 
are  found  to  have  the  same  taste.  Many  of  the  carbon  com- 
pounds have  a  distinct  sour  taste.  Moreover,  all  the  solu- 
ble chlorides  are  found  to  be  salt  (like  table  salt) ;  only 
with  the  highest  members  in  the  series  of  compounds  the 
taste  becomes  more  saline  and  develops  into  a  bitter. 
Many  sweet  substances  are  alcoholic  bodies,  and  contain  the 
radical  CH2OH. 

On  data  such  as  the  foregoing  it  has  been  claimed l  that 
tastable  bodies  are  surrounded  by  vibrating  matter  which 
acts  on  the  sensitive  surfaces  of  the  organ ;  and  that  the 
1  For  example,  by  J.  B.  Haycraft,  in  Brain,  July,  1887. 


236  PHYSIOLOGICAL   PSYCHOLOGY. 

quality  of  the  sensation  is  dependent  upon  the  character 
of  the  vibrating  matter.  Just  as  a  certain  class  of  salts  of 
allied  physical  and  chemical  properties  vibrate  in  a  certain 
way,  and  stimulating  the  eye,  produce  the  same  color-sensa- 
tions ;  just  so  do  similar  sapid  compounds,  which  contain 
elements  of  the  same  compound  radical,  vibrate  in  similar 
way  and  produce  the  same  taste.  Apparent  exceptions  to 
the  simpler  laws  may  be  due  to  the  fact  that  the  tongue, 
like  the  eye,  has  no  power  of  analysis.  The  same  taste 
may  then  be  produced  by  a  simple  vibration,  or  by  a  com- 
pound of  simple  vibrations. 

Classification  of  Tastes.  —  Sensations  of  this  sense  are,  in 
ordinary  experience,  combined  with  those  of  smell,  touch, 
temperature,  common  feeling,  and  the  muscular  sense.  It 
has  been  customary  to  distinguish  at  least  four  specifically 
different  sensations  of  taste,  —  namely,  sour,  sweet,  salt, 
and  bitter.  To  them  Wundt  would  add  the  alkaline  and 
the  metallic.  All  other  so-called  tastes  are  then  supposed 
to  be  compounds  of  these  specific,  simple  sensations  of  taste 
with  one  another,  and  with  the  other  kinds  of  sensations 
mentioned  above.  It  seems  very  doubtful,  however,  whether 
this  classification  will  satisfy  all  the  experiences  we  have 
under  this  sensation.  In  consciousness,  the  sensations  of 
this  sense,  like  those  of  color  and  light,  are  not  analyzable 
into  so  few  simple  elements.  The  sensations,  as  such  — 
that  is  to  say  —  are  not  exhaustively  classified.  Moreover, 
the  similarity  of  our  sensations  of  taste  to  those  of  smell, 
in  respect  of  their  bewildering  variety,  is  quite  too  marked 
to  make  us  satisfied  with  any  of  the  existing  schemes  of 
classification. 

SENSATIONS  OF  THE  SKIN,  MUSCLES,  JOINTS,  ETC., 
Q  UALITA  TIVEL  T  CONSIDERED. 

At  least  two  specifically  different  sensations  —  namely, 
Pressure  and  Temperature  —  have  generally  been  admitted 


QUALITY   OF   SENSATIONS. 


237 


to  have  their  organ  in  the  skin.  It  is  only  recently,  how- 
ever, that  the  sensations  arising  by  irritation  of  this  organ 
have  been  discriminated  and  discussed,  in  a  thorough  man- 
ner, by  experimental  means  of  investigation.  In  general, 
it  should  be  said  that  many  of  the  sensations  which  we 
localize  in  the  skin  are  really  of  cerebral  origin,  and  result 
from  the  compounding  of  a  variety  of  sensory  impulses, 
in  the  appropriate  way,  within  the  cerebral  centres. 

Excitable  Regions  for  Sensations  of  Pressure.  —  The  so- 
called  "  feelings,"  or  more  properly  sensations  of  pressure, 
are  dependent  upon  the  excitation  of  the  sensory  nerves  of 
the  skin  through  their  end-organs.  The  excitation  of  the 
trunk  of  these  nerves  produces  sensations  of  pain,  but  not 
those  definite  sensations  of  touching  and  being  touched, 
which  we  are  able  so  definitely  to  localize. 


FIG.  73.  —  Arrangement  of  Pressure-spots  (Goldscheider).  A,  dorsal  and  radial  sur- 
face of  the  first  phalanx  of  the  index  finger;  B,  membrane  between  thumb  and  index 
finger;  C,  dorsal  surface  of  fore-arm;  D,  back;  E,  inner  surface  of  fore-arm;  F,  back  of 
hand. 

It  is  a  comparatively  recent  discovery  that  the  definite 
pressure-sensations  are  aroused  only  by  exciting  minute 
areas  of  the  skin  called  "  pressure-spots."  These  spots  are 


238  PHYSIOLOGICAL  PSYCHOLOGY. 

arranged  in  a  manner  somewhat  like  that  of  the  "  tempera- 
ture-spots" (to  be  explained  subsequently).  They  are 
placed  in  chains,  as  it  were,  sometimes  more  and  some- 
times less  thickly  set.  These  chains  ordinarily  radiate 
from  a  kind  of  central  point,  and  run  so  as  to  form  circu- 
lar, or  pyramidal,  or  longitudinal  figures.  They  are  most 
numerous  in  the  areas  of  the  skin  most  sensitive  to  pres- 
sure. The  different  spots  differ  in  regard  to  sensitiveness ; 
some  are  much  more  easily  excited  than  others. 

Distinctions  in  Pressure-sensations,  —  The  investigations 
of  Goldscheider  lead  him  to  distinguish  two  specifically 
different  sensations  which  enter  into  what  is  ordinarily 
called  the  "  feeling  of  pressure."  If  a  very  fine  point  of 
metal,  wood,  or  cork,  be  touched  lightly  to  the  skin,  it  will 
be  found  to  awaken  a  definite  sensation  only  at  certain 
minute  spots.  This  sensation,  when  the  pressure  is  light, 
is  very  lively  and  delicate,  and  is  often  accompanied  by 
the  feeling  of  being  tickled.  On  increasing  the  pressure, 
however,  the  sensations  change  their  character;  the  feel- 
ing becomes  as  though  a  small  hard  kernel  were  pressed 
against  the  skin.  Between  these  spots  it  is  not  possible 
by  pressure  to  excite'  the  same  characteristic  sensations. 
Stimulation  of  the  spaces  between  the  pressure-spots  pro- 
duces a  dull,  indefinable,  "  contentless  "  sensation  ;  and,  if 
the  pressure  is  increased,  a  feeling  of  being  pricked  or 
stuck. 

In  respect  to  quality,  pure  and  simple,  sensations  of 
pressure  scarcely  admit  of  further  classification.  We 
localize  them  in  the  general  field  of  touch ;  but  we  do  not 
recognize  kinds  of  them,  as  we  do  in  the  case  of  sensations 
of  smell  and  taste.  The  distinction  between  "  light  touch  " 
and  "  sensations  of  weight "  is  one  of  degrees  of  compound 
sensations  involving  the  muscles  and  joints,  etc.,  as  well  as 
the  skin.  As  simple  sensations,  they  differ  in  intensity 
rather  than  in  quality  strictly  so-called. 


QUALITY   OF   SENSATIONS.  239 

The  attempt  has  sometimes  been  made  to  identify  sen- 
sations of  light  touch  with  sensations  of  temperature. 
Weber  held  that  cold  bodies  resting  on  the  skin  appear 
heavier  than  they  are,  and  warm  bodies  lighter.  One  sil- 
ver dollar  of  the  temperature  of  25°-19i°  F.  appeared 
as  heavy  as  two  dollars  of  98i°-100^°.  The  same  conclu- 
sion has  been  drawn  from  the  observation  that  it  is  difficult 
to  distinguish,  in  certain  parts  of  the  skin  when  irritated 
through  a  square  opening  in  a  piece  of  paper,  whether  the 
cause  of  the  irritation  is  a  light  brush  from  cotton  or  the 
approach  of  a  slightly  heated  surface.  But  small  wooden 
disks,  when  heated  to  122°  F.,  were  found  by  another 
observer  to  feel  heavier  than  really  larger  ones  when  not 
warmed.  And  even  if  the  same  stimuli  could  be  used  to 
excite  either  one  of  these  two  classes  of  sensations,  the 
qualitative  distinctness  of  the  sensations  themselves  would 
not  be  impaired.  Moreover,  cases  have  been  reported  where 
areas  of  the  skin  suffering  from  a  complete  loss  of  sensi- 
tiveness to  light  pressure  have  been  more  highly  sensitive 
than  was  normal  to  sensations  of  temperature. 

Excitable  Regions  for  Temperature-sensations.  —  Certain 
minute  areas,  and  these  only,  are  susceptible  to  irrita- 
tions of  a  kind  to  result  in  sensations  of  .heat  and  cold. 
Such  spots  are  insensible  to  pain  and  probably  also  to  pres- 
sure. Moreover,  some  of  these  minute  areas  are  sensitive 
to  cold  only  ("  cold-spots  ")  ;  others  of  them  to  heat  only 
("heat-spots").  When  the  topography  of  the  skin  is 
carefully  mapped  out,  these  two  kinds  of  temperature-spots 
appear  not  to  be  superimposed.  They  are  not  located 
alike  on  the  symmetrical  parts  of  the  two  sides  of  the 
same  individual,  nor  on  the  corresponding  parts  of  differ- 
ent individuals.  In  general,  they  occur  in  lines  that  radi- 
ate from  centres  coincident  with  the  roots  of  the  hairs. 
These  lines  often  cross  each  other  and  form  figures  of  vari- 
ous shapes.  Heat-spots  are,  on  the  whole,  less  numerous 


240 


PHYSIOLOGICAL   PSYCHOLOGY. 


than  cold-spots ;  but  in  parts  of  the  body  where  the  skin 
is  most  sensitive  to  either  temperature,  the  corresponding 
kind  of  spots  is  most  numerous.  "  Temperature-spots " 
have  been  divided  into  first  class  and  second  class,  accord- 


FIG.  74.  —  Arrangement  of  Temperature-spots, 
from  the  palm  of  the  left  hand  (Goldscheider). 


A,  heat-spots;  and  B,  cold-spots  — 


ing  to  the  degree  of  strength  with  which  they  react  on 
moderate  stimulation.  Some  of  them  are  irritated  only  by 
excessive  temperatures.  The  same  temperature  may  seem 
ice-cold  to  one  spot  and  only  cool  to  another. 

Stimulus  of  Temperature-sensations.  —  Whatever  form  of 
energy  excites  the  nerves  of  the  skin  at  the  "  heat-spots  " 
or  "  cold-spots  "  calls  forth  the  specific  sensations  corre- 
sponding to  these  spots.  Thus,  the  electrical  current,  or 
puncturing  the  skin  with  a  point,  may  be  felt  as  either 
cold  or  hot,  respectively.  Among  the  inducements  to 
sensations  of  heat,  the  following  have  been  mentioned  by 
Hering  as  the  more  ordinary:  All  checking  of  the  radia- 
tion of  heat  when  the  blood-supply  remains  unaltered ;  all 
contact  with  a  medium  or  an  object  of  higher  temperature ; 
all  increase  to  the  heat  of  the  skin  coming  from  the  interior 
of  the  body.  On  the  contrary,  different  areas  of  the  skin 
feel  cold,  when  the  convection  of  the  heat  from  the  skin 
increases  while  the  blood-supply  remains  unchanged ;  when 
there  is  contact  with  objects  that  have  the  same  tempera- 
ture as  the  air,  but  convey  the  heat  more  rapidly  than  it ; 
on  contact  or  proximity  to  objects  colder  than  the  skin ; 
and  on  lessening,  in  any  way,  the  interior  warmth  of  the 
body. 


QUALITY   OF   SENSATIONS.  241 

Laws  of  Excitation  for  Temperature-sensations.  —  It  is 
difficult  to  bring  the  recent  discoveries  in  physiological 
psychology,  regarding  the  origin  and  nature  of  tempera- 
ture-sensations, into  any  relation  with  the  physics  of  objec- 
tive heat  as  a  mode  of  motion.  It  will  be  seen  (when  we 
come  to  consider  the  perceptions  that  arise  through  these 
sensations  in  part)  that  psycho-physical  principles  —  such 
as  those  of  contrast,  relativity,  exhaustion,  etc.  —  have  a 
large  share  in  determining  the  character  of  this  class  of 
our  particular  experiences. 

Sensations  of  temperature  seem  also  to  have  a  certain 
dependence  on  the  temperature  of  the  thermic  apparatus 
itself.  This  law  has  thus  been  stated  by  its  leading  expo- 
nent: "  As  often  as  the  thermic  apparatus  at  any  point  in  the 
skin  has  a  temperature  which  lies  above  its  own  zero-point 
we  have  a  sensation  of  heat ;  in  the  contrary  case,  a  sen- 
sation of  cold.  Either  sensation  is  so  much  the  more 
marked  or  stronger,  the  more  the  temperature  of  the  ther- 
mic apparatus  at  the  time  varies  from  the  temperature  of 
its  own  zero-point."  [By  the  "  zero-point  "  of  any  part  of 
the  skin  is  meant  the  exact  objective  temperature  which  at 
that  part  will  produce  no  sensation  of  either  heat  or  cold.] 
According  to  this  principle  it  is  proposed  to  explain  all 
our  ordinary  sensations  of  temperature. 

The  earliest  great  observer  in  this  field  (E.  H.  Weber) 
thought,  however,  that  all  rising  of  the  temperature  of  the 
skin  is  felt  as  heat,  and  its  sinking  as  cold.  Thus,  if  we 
hold  one  hand  in  moderately  cold  water,  and  dip  the  other 
repeatedly  in  the  same  water,  the  sensation  of  cold  is 
stronger  in  the  latter,  although  the  temperature  of  the 
hand  held  constantly  in  the  water  is  the  lower.  Yet  the 
most  important  recent  observer  (Goldscheider)  calls  atten- 
tion to  an  experiment  which  shows  that,  if  one  hand  be 
left  for  ten  seconds  in  water  of  the  temperature  of  104°  F., 


242  PHYSIOLOGICAL  PSYCHOLOGY. 

and  then  both  hands  immersed  in  cold  water,  the  warmed 
hand  will  feel  the  cold  less  distinctly  than  the  other. 

Our  perception  of  the  absolute  degree  of  temperature, 
and  of  minute  variations  in  temperature,  is  most  acute  for 
places  in  the  scale  lying  close  to  the  normal  temperature 
of  the  skin.  It  must  be  confessed  that  the  exact  manner 
in  which  changes  of  objective  temperature  act  upon  the 
thermic  apparatus  to  excite  it  is  unknown.  Possibly  the 
immediate  stimulus  of  this  apparatus  consists  of  some  form 
of  chemical  or  electrical  energy  developed  by  the  increase 
and  decrease  of  that  molecular  motion  which  physics  calls 
"  heat." 

The  question  whether  qualitatively  distinct  sensations 
arise  in  the  mind  through  irritation  of  sensory  nerves 
seated  in  the  muscular  fibre  has  been  much  debated.  In 
our  judgment,  however,  valid  reasons  may  be  given  for 
maintaining  the  existence  of  Muscular  Sensations.  Most 
of  the  evidence  in  proof  of  this  position  properly  belongs 
in  connection  with  the  development  of  complex  percep- 
tions of  the  position  and  movement  of  the  eye,  the  limbs, 
etc. 

Existence  of  Sensations  of  the  Muscular  Sense,  —  For  some 
time  it  was  disputed  whether  the  muscular  fibres  are  di- 
rectly connected  with  sensory  nerve-fibrils.  In  1874  Sachs 
apparently  demonstrated  the  affirmative  of  this  disputed 
question.  The  psychological  evidence  for  muscular  sen- 
sations is  partly  immediate,  and  based  upon  the  testimony 
of  consciousness,  and  partly  indirect  and  experimental. 

It  can  scarcely  be  doubted  that  we  localize  certain  mas- 
sive sensation-complexes  in  the  muscles  of  the  different 
parts  of  the  body.  This  impression  is  peculiarly  fresh 
and  strong  when,  attending  carefully  to  our  sensations, 
we  lift  weights,  or  take  positions,  which  call  into  action 
unused  muscles  of  the  limbs  or  trunk.  In  itself  con- 
sidered, little  stress  might  be  laid  upon  this  appeal  to  the 


QUALITY  OF   SENSATIONS.  243 

immediate  testimony  of  consciousness  on  a  psycho-physical 
question.  But  it  will  become  apparent  by  our  subsequent 
study  of  perception  that  the  theoretical  need  of  muscular 
sensations,  in  order  to  account  for  the  knowledge  of  the 
developed  mind,  confirms  the  testimony  of  consciousness. 

Moreover,  experiment  and  observation  of  the  more  care- 
ful scientific  sort,  on  the  whole,  favor  the  assumption  of  a 
muscular  sense,  whose  sensations  vary  in  the  quality  which 
they  assume  in  the  conscious  life  of  the  mind.  For  in- 
stance, there  seems  to  be  no  regular  parallelism  between 
the  loss  of  the  other  modes  of  sensibility  and  the  loss  of 
muscular  sense-impressions.  In  rare  cases,  in  what  is 
called  "  locomotor  ataxy,"  there  may  be  little  loss  of  ordi- 
nary sensibility  and  yet  a  marked  deprivation  of  muscular 
sense.  On  the  other  hand,  sensibility  of  the  skin  may  be 
impaired  or  destroyed  without  impairing  the  ability  to  dis- 
criminate weights  when  the  muscles  are  moved. 

A  recent  experimenter  found  that,  after  temporary 
destruction  with  cocain,  of  the  sensibility  of  the  larynx 
and  vocal  cords,  a  singer  could  sing  almost  (if  not  quite) 
as  accurately,  as  respects  pitch,  as  before.  With  what  did 
this  singer  guide  his  voice,  if  not  with  the  muscular  sen- 
sations and  their  memory-images?  Another  observer 
reports  the  case  of  a  patient  who  had  lost  an  area  of  skin, 
10x12  centimeters,  without  any  influence  on  the  muscular 
sensibility  of  the  subjacent  contractile  bodies. 

Nature  and  Kinds  of  Muscular  Sensations,  —  The  precise 
manner  in  which  the  muscular  sensations  are  originated, 
by  excitation  of  the  sensory  nerve-fibrils  lying  within  the 
muscles,  is  unknown.  The  stimulus  immediately  acting  on 
these  end-organs  might  be  conceived  of  as  either  mechani- 
cal or  chemical,  or  electrical.  It  can  scarcely  consist 
in  the  mere  irritation  caused  by  the  molecular  changes 
that  accompany  the  contraction,  tension,  and  relaxation  of 
the  muscles,  We  do  not  see,  however,  that  our  ignorance 


244  PHYSIOLOGICAL   PSYCHOLOGY. 

of  the  manner  in  which  degrees  of  pressure  act  to  produce, 
through  the  end-apparatus  of  sense,  different  qualities  of 
sensation,  is  much  more  profound  in  the  case  of  the 
muscles  than  in  the  case  of  the  skin. 

It  must  also  be  confessed  that  muscular  sensations  are 
very  difficult  of  analysis  by  the  method  of  self-conscious- 
ness. In  consciousness  they  exist  as  complexes,  entangled 
with  sensations  that  arise  through  irritation  of  the  "  pres- 
sure-spots "  and  "temperature-spots"  of  the  skin,  and  in 
the  joints,  etc.  Moreover,  muscular  sensations,  of  them- 
selves, seem  to  differ  chiefly  in  "  extensity,"  and  quantity, 
or  intensity,  rather  than  in  quality.  It  is  only  as  already 
localized,  and  combined  with  sensation-complexes  of  other 
kinds,  that  the  muscular  sensations  admit  of  being  dis- 
tinguished as  respects  quality. 

To  this  very  difficult  subject  we  shall  return  in  other 
connections. 

Sensations  of  the  Joints,  Tendons,  etc.  —  Experimental  evi- 
dence has  tended  to  show  that  certain  kinds  of  sensations, 
of  value  in  our  perceptions  of  the  positions  and  motions  of 
the  body,  originate  in  the  joints.  Goldscheider  experi- 
mented by  resting  the  hand,  palm  upward,  in  a  plaster  cast, 
bending  the  index  finger  back  by  changing  the  pressure  of 
a  small  weight,  and  then  measuring  the  least  angle  of  bend- 
ing which  could  be  perceived  at  the  first  joint.  By  a 
faradic  current  complete  insensibility  of  the  joint  was  then 
produced.  It  was  now  found  that  the  finger  must  be  bent 
farther  than  before  in  order  to  have  its  flexure  perceived. 
Sensations  produced  by  irritating  the  nerves  of  the  joint 
would  appear,  then,  to  enter  into  the  perception  of  the 
movements  of  the  finger.  It  has  also  been  discovered  that 
ataxic  persons  can  recognize  slow  movements  of  the  limbs 
with  short  excursions,  if  accompanied  by  pressure  on  the 
joints ;  otherwise  not. 

Various    Unclassified    Sensations.  —  Experiments    with  a 


QUALITY   OF   SENSATIONS.  245 

travelling  metallic  point,  carrying  the  stimulus  of  a  cur- 
rent of  electricity  over  the  skin,  reveal  an  astonishing 
diversity  of  sensations  awakened  at  different  points  of  the 
surface.  .  "Thrill-points,"  "tickle-points,"  and  points  of 
cutting  pain,  are  all  thus  distinguished  through  irritation 
of  the  same  stimulus.  Places  occur  where  the  rate  of 
motion  seems  suddenly  to  increase  without  any  objective 
increase  of  its  rate  ("  acceleration-points  ")  ;  other  places 
occur  where,  although  continuing  to  move  with  uniform 
velocity,  the  travelling  point  seems  to  stop  ("  blind-spots  " 
of  the  skin).  Strange  tangles  of  sensation,  from  which 
unaccustomed  sensations  can  be  partially  disentangled, 
spring  up  in  consciousness. 

"Sensations  of  motion"  are  sometimes  spoken  of  as 
though  they  formed  a  distinct  kind.  This  we  believe  to  be 
incorrect.  Without  a  succession  of  qualitatively  different 
sensation-complexes  arising  in  consciousness,  no  perception 
of  motion  can  occur.  This  perception  is,  however,  pecul- 
iarly fundamental  and  instinctive,  as  it  were. 

THE  QUALITY  OF  SENSATIONS  OF  SOUND. 

There  are  two  kinds  of  sounds  —  tones,  or  musical  sounds, 
and  noises.  The  latter  are  those  sounds  which  are  wanting 
in  periodic  regularity  of  stimulation  and  in  the  peculiar, 
pleasant  modification  of  consciousness  which  tones  have. 
Tones  and  noises  are  actually  blended  in  nearly  or  quite 
all  sounds.  Noises  may  be  compounded  out  of  musical 
sounds,  as,  for  example,  by  striking  at  once  all  the  notes  of 
an  octave  upon  a  piano-forte.  Noises  are  not  easily  class- 
ifiable and  are  of  little  interest  either  to  physical  or  to 
psychological  science.  Hensen  has,  however,  distinguished 
three  "  categories  of  unmixed  noises  " ;  these  are  the  "  beats  " 
(or  pulsations  which  disturb  the  purity  of  some  musical 
tone),  the  crackle,  crack  or  crash,  and  the  hissing  noises. 

Nature  of  the  Musical  "  Clang."  —  The  tones  of  ordinary 


246  PHYSIOLOGICAL  PSYCHOLOGY. 

experience  are  complex  sensations.  They  result  from  the 
blending  of  several  simple  tones  into  one  compound  tone. 
This  blending  is  not  so  complete,  however,  that  a  trained 
ear  cannot  analyze  it.  For  the  complex  musical  sounds 
of  ordinary  experience  we  borrow  from  the  German  usage 
the  word  "  clang."  The  quality  of  tones  considered  as 
simple  sensations  is  their  pitch,  which  is  spoken  of  as 
"high"  or  ulow,"  according  to  the  place  which  we  assign 
to  our  acoustic  sensations  as  immediately  apprehended,  and 
compared  together,  in  consciousness.  The  quality  of  the 
complex  tones,  or  "clangs,"  is  the  so-called  timbre,  or 
"  tone-color." 

The  Pitch  of  Simple  Tones.  —  It  has  been  said  that  the 
quality  of  simple  musical  sounds  is  their  "pitch."  Sub- 
jectively considered,  this  quality  is  immediately  determined 
by  the  place  we  assign  the  tone  in  a  musical  scale.  In  this 
scale  —  for  reasons  to  which  reference  will  subsequently 
be  made  —  we  fix  all  notes  as  higher  or  lower,  on  comparison 
of  their  characteristic  quality.  Objectively  considered,  the 
pitch  of  tones  depends  upon  the  rapidity  of  the  periodic 
vibrations  (the  number  in  a  given  unit  of  time,  usually 
one  second)  which  occasions  them,  or,  what  is  the  same 
thing,  it  depends  upon  the  length  of  the  sound-waves. 

The  pitch  of  tones  is  theoretically  determined  by  meas- 
uring the  number  of  vibrations  found  necessary  to  produce 
some  characteristic  musical  sound  which  it  is  convenient 
to  select  as  a  fixed  point  in  the  musical  scale.  The  place 
of  the  other  tones  may  then  be  fixed  with  relation  to  this 
tone  selected  as  a  point  of  starting,  according  to  those 
simple  numerical  relations  between  the  tones  with  which 
physics  has  made  us  familiar.  Thus,  in  the  German  scale 
the  tone  of  the  pitch  called  a1  is  fixed  at  440  vibrations  in 
a  second.  The  French  scale  fixes  the  same  tone  at  435 
vibrations,  and  the  theoretical  pitch  in  England  gives  512 
vibrations  for  c2. 


QUALITY   OF   SENSATIONS.  247 

Limits  of  Pitch.  —  Sensations  of  musical  sound  have  both 
an  upper  and  a  lower  limit ;  that  is  to  say,  vibrations  either 
below  or  above  a  certain  number  per  second  produce  no 
sensations  of  musical  sound  at  all.  The  difficulties  of 
determining  these  limits  are  great,  and  considerable  allow- 
ance must  be  made  for  individual  peculiarities.  Some 
persons  can  discern  tones  of  a  pitch  below  or  above  those 
tones  audible  to  others.  Helmholtz  thought  that  the  tone 
(or  musical  quality)  of  the  sound  begins  to  fade  out  when 
the  vibrations  are  fewer  than  34  per  second.  Tuning-forks, 
vibrating  28  times  in  a  second,  have  been  heard  as  a  weak 
drone.  Preyer,  however,  considered  that  16  vibrations 
enabled  him  to  hear  a  tone.  For  most  ears  vibrations 
slower  than  28  to  32  per  second  make  only  a  buzzing  or 
groaning  noise. 

The  majority  reach  the  upper  limit  of  pitch  when  list- 
ening to  tones  produced  by  20,000  to .  22,000  per  second. 
Some  persons  can,  however,  hear  musical  sounds  produced 
by  30,000  or  40,000  vibrations  in  a  unit  of  time.  Perhaps 
in  certain  very  sensitive  ears  the  upper  limit  may  be  placed 
as  high  as  50,000.  More  acute  tones  than  these  are 
unpleasant  noises,  and  finally  become  inaudible. 

The  range  of  the  average  human  ear  is  rather  more  than 
nine  octaves  of  pitch,  —  reaching  from  about  A2  of  the  sub- 
contra  octave  (27^  vibrations,  German  scale)  to  above  c1  of 
the  seven-times-marked  octave  (16,896). 

Sensitiveness  to  Differences  of  Pitch.  —  Preyer  found  that 
unpractised  persons,  experimenting  with  the  octaves  lying 
in  the  middle  of  the  musical  scale  (from  c  to  c2),  distinguish 
a  difference  in  pitch  corresponding  to  from  8  to  16  vibra- 
tions per  second.  A  few  are,  however,  so  "  deaf  "  to  pitch 
that  an  interval  of  less  than  a  musical  "  third,"  or  even,  in 
the  higher  and  lower  parts  of  the  scale,  a  "seventh,"  is 
indistinguishable.  If  a  person  is  insensitive  to  differences 
of  less  than  a  tone  or  a  semi-tone,  he  may  be  said  "  not  to 


248  PHYSIOLOGICAL   PSYCHOLOGY. 

know  one  note  from  another."  In  a  trained  musical  ear 
the  sensitiveness  may  be  much  greater  than  that  men- 
tioned above.  Thus,  in  the  range  most  easily  covered  by 
the  human  voice  (cl  to  e3)  successive  notes  can  be  distin- 
guished, as  respects  pitch,  when  they  differ  by  not  more 
than  i,  or  even  \  and  -|-,  of  a  single  vibration.  Thus,  where 
the  piano  gives  24  notes,  the  ear  can  perhaps  distinguish 
3000.  But  in  the  upper  limits  of  the  scale  (e.g.  above  c6) 
well-trained  ears  may  identify  notes  that  differ  by  100,  or 
even  by  1000,  vibrations  per  second. 

Distinctions  in  Purity  of  Interval.  —  Individuals  differ 
greatly  in  their  ability  to  tell  when  two  notes  of  different 
pitch  have  just  the  right  amount  of  interval.  This  ability 
varies  in  all  persons  for  different  intervals.  Thus,  if  the 
sensitiveness  of  the  trained  ear  for  the  purity  of  the  inter- 
val of  an  octave  were  denoted  by  5000,  that  for  the  purity 
of  the  interval  called  "  the  fifth  "  would  be  822 ;  for  "  the 
fourth,"  211 ;  for  the  "  major  third,"  198 ;  for  the  "  minor 
third,"  117 ;  etc. 

Judgments  of  Absolute  Tone.  —  We  have  already  said  that 
discernment  of  difference  in  the  pitch  of  tones  is  immediate ; 
and  that  an  appeal  to  consciousness  indicates  the  place  to 
which  each  note,  in  comparison  with  other  notes,  shall  be 
assigned  in  the  musical  scale.  But  discernment  of  the 
absolute  pitch  of  a  musical  sound  is  a  very  complex  and 
difficult  operation,  dependent  upon  natural  "good  ear" 
and  upon  training.  One  observer  (Stumpf)  found,  by 
experimenting  upon  four  persons,  all  musicians,  that  only 
one  of  them  seemed  even  to  approach  infallibility. 

Means  for  Discernment  of  Pitch.  —  The  trained  musician 
can  put  several  hundred  tones,  distinguished  in  pitch  by 
the  ear,  between  the  notes  sounded  by  two  white  keys  of 
a  piano,  at.  the  most  favorable  parts  of  the  scale.  But 
Jenny  Lind  scarcely  succeeded  in  singing  in  quarter-tones. 
It  would  seem  then  that  the  muscular  sensations  connected 


QUALITY   OF   SENSATIONS.  249 

with  forming  or  apprehending  the  quality  of  musical 
sounds  do  not  furnish  our  sole  means  for  discriminating 
differences  of  quality.  This  power  seems  to  be  an  imme- 
diate comparison  of  the  tones,  as  heard,  in  our  conscious- 
ness. 

Formation  of  the  Scale  of  Pitch.  —  The  arrangement  of 
musical  sounds  in  a  series  called  a  "  scale  "  depends  upon 
an  immediate  power  of  the  mind  to  discern  the  difference 
in  characteristic  quality  between  any  two  notes  when  com- 
pared. This  arrangement  is  conveniently  symbolized  by  a 
series  of  different  positions  assigned  along  a  straight  line. 
Of  any  three  unlike  tones,  one  must  be,  and  only  one  can 
be,  arranged  as  respects  pitch  between  the  other  two. 
Whenever  any  two  tones,  as,  for  example,  m  and  w,  are 
given,  another  "sliding"  tone  which  begins  with  m  and 
ands  with  n  is  possible.  In  this  respect  the  scale  of  musi- 
cal sound  is  —  as  we  shall  see  —  different  from  that  of  the 
varying  shades  of  color.  There  are  two  ways  of  going 
from  yellow  to  blue  (i.e.  through  green  and  blue-green,  or 
through  violet,  red,  and  orange) ;  but  there  is  only  one 
way  of  getting  from  a1  to  c3  (viz.  through  £2,  c2,  d\  etc.). 
The  series  of  tones  is  therefore  spoken  of  as  a  continuous 
and  infinite  series. 

The  terms  which  we  apply  to  the  relations  as  respects 
quality,  of  the  musical  sounds  in  the  scale  —  "high," 
"low,"  "intervals,"  etc.  —  are  taken  from  the  complex 
tactual,  muscular,  and  visual  sensations  which  accompany 
and  fuse  with  the  acoustic.  In  sounding  the  so-called 
"  lower  "  tones,  the  vocal  organs  are  depressed ;  in  sound- 
ing the  "  higher,"  they  are  elevated.  Low  notes  make  in 
consciousness  the  impressions  of  breadth  and  gravity  which 
correspond  to  the  foundations  of  a  spatial  structure.  In 
reading  the  musical  scale  by  sight,  we  look  up  for  notes  of 
the  higher  pitch,  down  for  those  of  the  lower  pitch.  In 
playing  on  stringed  instruments,  the  hands  are  correspond- 


250  PHYSIOLOGICAL  PSYCHOLOGY. 

ingly  moved.  Properly  speaking,  however,  differences  of 
pitch  are  not  representable  as  relations  of  space.  In  other 
words,  the  terms  applied  to  such  differences  all  result  from 
associated  mental  impressions. 

The  Timbre  of  "Clangs."  —  When  any  single  note  is 
sounded  on  a  musical  instrument,  or  by  the  voice,  the 
result  is  a  "  clang,"  or  composite  musical  sound.  This 
clang  may  be  objectively  regarded  as  the  summing-up  of 
the  waves  of  a  fundamental  tone  (the  simple  tone  of  the 
note  sounded)  and  the  waves  of  certain  partial  tones 
belonging  to  the  fundamental  tone.  The  stimulus  which 
occasions  the  complex  sensation  is,  then,  a  complex  sound- 
wave. The  composite  quality  of  each  "clang"  depends 
upon  the  character  of  this  complex  sound-wave. 

We  have  seen  that  each  sensation  among  the  ordinary 
musical  "  tones  "  is  composed  in  consciousness  of  several 
absolute  qualities  of  simple  tones.  Every  "  clang "  may 
be  subjectively  regarded  as  the  fusion,  more  or  less 
complete,  in  consciousness,  of  the  simple  and  qualitatively 
unlike  tones  corresponding  to  the  composite  acoustic 
waves.  These  partial  tones,  or  "  over-tones,"  are  the 
"  harmonics "  of  the  clang,  or  single  compound  tone. 
This  composite  quality  or  "  coloring "  of  the  note  thus 
produced,  and  which  is  different  for  different  instruments 
and  voices,  is  called  its  "  timbre."  It  is  dependent  upon 
the  number,  pitch,  and  relative  strength  of  the  simple 
tones  which  are  compounded  into  the  "  clang." 

Thos.e  simple  tones,  whose  vibrations  stand  in  simple 
mathematical  relations  when  combined  into  a  "  clang," 
produce  in  consciousness  a  peculiar,  pleasant  sensation; 
those  whose  vibrations  stand  in  complex  mathematical 
relations,  when  combined,  produce  an  unpleasant  sensation. 
Thus  the  eight  different  notes  of  every  octave  stand  in  the 
following  relations  to  each  other :  — 


QUALITY   OF   SENSATIONS.  251 

C:D:E  :  F:  G  :  A   :  B  :  C1 

l:f:f  :   f  :|       I    '•*£'.  2 
8  :  9  :  10  :  lOf  :  12  : 13i  :  15  : 16 

That  is  to  say,  while  the  tone  0  makes  one  vibration,  the 
tone  D  makes  £ ,  and  E  makes  j,  etc. ;  or  while  O  makes 
8  vibrations,  D  makes  9,  E  makes  10,  etc. 

Consonance  and  Dissonance.  —  When  two  or  more  "  clangs  " 
are  sounded  together,  the  result  is  a  highly  complex  sen- 
sation, with  a  characteristic  pleasant  or  unpleasant  feeling 
attached.  If  the  feeling  is  pleasant,  the  resulting  complex 
of  fused  sensations  is  called  a  "  consonance  "  or  "  chord  " ; 
if  the  feeling  is  unpleasant,  it  is  a  "  dissonance  "or  "  dis- 
cord." Thus  c  and  cl  struck  together  make  a  pleasant 
combination  of  "clangs";  c  and  d,  or  c  and  c  sharp,  ore 
and  its  seventh,  b  above,  make  an  unpleasant  and  discordant 
combination. 

Consonance  and  dissonance  differ  from  the  cases  of  com- 
bination, already  considered  as  belonging  to  every  "  clang," 
with  respect  to  the  relative  strength  of  the  partial  tones 
when  compared  with  the  fundamental  tones.  In  the 
clang  the  over-tones  are  weak  in  comparison  with  the 
fundamental  tone ;  in  the  chord,  or  discord,  the  fundamental 
tones  of  the  other  clangs  are  strong  and  stand  in  powerful 
relations  of  consonance  or  dissonance  toward  the  funda- 
mental tone  of  the  lowest  clang  among  them. 

There  are  degrees  of  consonance  and  dissonance  which 
depend  upon  the  amount  of  coincidence  or  disagreement 
belonging  to  the  acoustic  waves  of  the  different  tones 
which  are  combined.  With  the  relation  of  "the  Third" 
we  come  upon  the  borders  of  a  dissonance;  indeed,  the 
ancient  Greeks  and  Romans  regarded  the  Third  as  a  dis- 
sonance. The  major  Third  and  the  major  Sixth  are 
called  "  medial  consonances "  by  Helmholtz ;  the  minor 
Third  and  minor  Sixth  are  called  "imperfect  consonances." 
The  following  table  represents  these  differences :  — 


252  PHYSIOLOGICAL  PSYCHOLOGY. 

Octave  (1:2) 
Twelfth  (1 :  3) 
Fifth  (2 :  3) 

Founh  (3: 4)    {;|cy::;:g. 

Major  Third  (4:5)     {  ' 

L 


It  is  difficult  to  give  a  satisfactory  psycho-physical  cause 
for  the  characteristic  feelings  of  pleasure  and  pain  which  ac- 
company those  sensation-complexes  that  are  called  "chords" 
and  "  discords."  The  cause  assigned  by  Helmholtz  is  the 
absence  or  presence  of  "  beats."  It  is  found  that  the  feel- 
ing of  dissonance  is  much  increased  when  the  difference  in 
pitch  of  two  tones  that  lie  near  together  is  progressively 
diminished.  This  feeling  is  due  to  the  successive  shocks, 
called  "  beats,"  that  occur  as  the  pitch  of  the  tones  becomes 
more  nearly  the  same.  It  reaches  its  height  when  the 
number  of  the  beats  is  about  30  per  second.  For  example, 
if  b1  (495  vibrations,  in  German  scale)  and  c2  (528  vibra- 
tions) are  struck  together,  the  number  of  beats  is  33 
(528  —  495  =  8^v  and  the  dissonance  is  strongly  marked. 
The  feeling  of  consonance  Helmholtz  considers  to  be  due 
to  the  absence  of  beats.  This  reason  is,  however,  only  a 
negative  one. 

It  has  been  proposed  to  supplement  the  negative  reason 
given  above  by  a  positive  one.  The  pleasure  of  conso- 
nance is  thus  allied  to  that  which  follows  all  —  even  dim 
and  half-conscious  —  recognition  of  relations.  The  so- 
called  "  tonicity  "  —  or  property  of  being  recognized  as  a 
constituent  of  a  single  fundamental  tone  —  of  consonances 
is  thought  to  afford  the  reason  for  the  pleasant  feeling  con- 
sonances excite.  To  this  is  added  the  so-called  "  phonicity  " 


QUALITY   OF   SENSATIONS.  253 

of  the  consonances ;  and  by  this  is  meant  the  property 
which  consists  in  the  possession  of  certain  partial  tones 
that  are  common  to  all  tones. 

It  may  well  be  doubted  whether  these  explanations  really 
explain.  Indeed,  in  the  present  condition  of  our  knowl- 
edge^ we  are  obliged  to  consider  the  peculiar  and  charac- 
teristic pleasant  quality  of  consonances,  and  the  opposite 
quality  of  dissonances,  as  fundamental  and  inexplicable 
facts  of  our  primary  experience. 


CHAPTER   XL 

THE   QUALITY  OF  SENS'A TIONS.  —  Continued.  ' 

THE  analysis  of  the  qualities  of  Sensations  of  Sight  is 
much  more  intricate  than  that  of  any  of  the  other  senses. 
They  may  all  be  divided,  however,  into  sensations  of  color 
and  sensations  of  light.  But  as  we  shall  soon  see,  in  form- 
ing "  perceptions  "  of  sight  various  other  classes  of  sensa- 
tions are  closely  blended  with  those  of  color  and  light. 

Conditions  of  Experimenting.  —  In  order  to  determine 
under  what  conditions  the  quality  of  visual  sensations 
varies,  no  little  care  is  required.  Changes  in  quality  are 
found  to  be  dependent  upon  a  variety  of  causes  which,  as 
a  rule,  act  together,  but  cannot  be  discriminated  by  self- 
consciousness.  Quality  of  sensations  —  color,  for  example  — 
depends  upon  the  amount  of  white  light  which  is  mixed 
with  any  particular  "  spectral "  color.  Only  the  "  color- 
tones  "  derived  by  spectral  analysis  are  found  to  be  "  pure  " 
or  "  saturated."  (Probably,  as  we  shall  see  subsequently, 
even  these  are  not  perfectly  so.)  The  size  of  the  colored 
object,  and  the  resulting  extensity,  or  breadth,  of  the  sen- 
sation, affects  its  quality;  so  does  the  intensity  of  the 
stimulus,  and  the  time  during  which  it  acts.  The  same 
stimulus  also  produces  different  sensations  when  it  falls 
upon  different  areas  of  the  same  retina.  The  quality  of 
the  sensation  further  depends  upon  the  previous  condition 
of  the  retina. 

VISUAL   SENSATIONS  CONSIDERED   AS   RESPECTS   QUALITY. 

The  question  before  us  may  then  be  stated  in  the  follow- 
ing somewhat  complex  form  :  What  sensations  result  from 

254 


QUALITY  OF   SENSATIONS. 


255 


the  stimulation  of  a  sufficiently  small,  but  not  too  small,  area 
of  the  most  central  part  of  a  normal  retina,  for  a  given 
time,  when  it  is  not  fatigued,  and  the  eye  is  at  rest,  and 
with  neither  too  great  nor  too  small  intensity  of  a  given 
kind  of  light? 

Excitable  Areas  for  Visual  Sensations.  —  Sensations  of  light 
and  color  are,  so  far  as  their  peripheral  origin  is  concerned, 
occasioned  by  irritation  of  the  rod-  and  cone-layer  of  the 
retina.  Probably  each  element  of  this  structure  may  be 
regarded  as  an  isolated  sensitive  spot,  which  corresponds, 
on  the  one  side,  to  definite  excitations  from  appropriate 
stimuli ;  and,  on  the  other  side,  to  the  smallest  distinct 
sensations  of  light  and  color.  In  order  that  two  visual 
sensations  may  be  seen  as  separate,  and  lying  side  by  side, 
two  neighboring  retinal  elements  must  be  excited  by  the 
stimulus. 

This  view  is  confirmed  by  the  degree  of  accuracy  of 
which  the  trained  eye  is  capable.  Few  observers,  for  exam- 
ple, can  distinguish  two  stars  a  b  c 
as  two,  unless  they  are  apart 
from  60"  to  70",  —the  num- 
ber differing  for  different 
eyes.  The  angle  thus  covered 
corresponds  very  closely  to 
the  size  of  a  retinal  element, 
—  namely,  from  0.00438  mm. 
to  0.00526  mm.  Moreover, 
if  white  lines  be  drawn  on  a 
black  ground  so  closely  to- 
gether as  to  approximate  this  limit  of  vision,  they  will 
appear,  not  straight,  but  knotted  and  nicked  (see  Fig.  75). 
This  fact  is  due  to  the  action  of  the  stimulus  on  the  rods 
and  cones. 

Stimulus  of  Visual  Sensations.  —  The  ordinary  form  of 
stimulus  which  is  understood  to  act  directly  on  the  end- 


FIG.  75.  —  A  shows  the  appearance  of 
lines  drawn  very  closely  together,  which  is 
supposed  to  be  due  to  their  falling  upon  the 
nervous  elements  of  the  retina  in  the  man- 
ner shown  by  B. 


256  PHYSIOLOGICAL  PSYCHOLOGY. 

organs  of  vision  is  light,  —  or  certain  exceedingly  rapid 
oscillations  of  so-called  luminiferous  ether.  The  actual 
immediate  excitant  of  the  rods  and  cones  we  have  seen, 
however,  to  be  —  it  is  probable  —  certain  photo-chemical 
changes  of  an  unknown  character.  But  these  changes, 
and  so  the  sensations  of  color  and  light,  may  be  occasioned 
by  other  forms  of  stimulus  than  light. 

Mechanical  stimulus  of  the  eyeball  by  pressure  upon  it 
with  the  ringer  or  a  blunted  stick  results  in  the  production 
of  so-called  phosphenes,  —  disks  of  light  with  darkly  col- 
ored edges.  A  blow  on  the  head,  or  an  electrical  current, 
may  cause  optical  sensations.  The  quality  of  the  sensa- 
tions aroused  by  the  electrical  stimulation  seems  to  change 
with  the  direction  (ascending  or  descending)  of  the  cur- 
rent. The  retina  has  also  a  "  light  of  its  own  "  (Eigen- 
licM)  ;  for  its  nervous  elements  are  rarely  or  never  inactive, 
but  have  a  continuous  tonic  excitation.  This  "  own-light " 
is  very  changeable  and  seems  to  have  a  rhythmic  move- 
ment. It  is  probably  due  to  the  photo-chemical  changes 
produced  by  the  changing  character  and  amount  of  the 
blood-supply. 

In  this  connection,  we  may  note  the  remarkable  phe- 
nomena of  so-called  "color-audition."  In  rare  cases,  the 
hearing  of  a  sound  is  spontaneously  accompanied  by  the 
seeing  of  a  color,  which  varies  with  the  sound  heard.  A 
case  in  France  has  recently  been  reported  —  hereditary  in 
father,  and  in  son  and  daughter  —  where  the  vowels,  open 
or  mute,  when  pronounced,  provoked  definite  color-sensa- 
tions. Thus,  a,  a'  and  d,  excited  the  sensation  of  red  or 
salmon  color ;  e,  e\  or  e,  of  white  ;  i,  of  black,  etc.  Certain 
obscure  cerebral  peculiarities  seem  to  be  implied  in  idio- 
syncrasies of  sight  like  this. 

The  Various  Color-tones.  —  It  has  already  been  said  that 
only  by  use  of  the  spectrum  can  we  obtain  "pure"  or 
"  saturated  "  color-tones.  This  instrument,  on  account  of 


QUALITY  OF   SENSATIONS. 


257 


the  different  refrangibility  of  the  different  colored  rays 
which  compose  the  compound  ray  of  white  light,  is  able 
to  analyze  the  color-tones.  It  is  thus  discovered  that  the 
compound  sensation  produced  by  sunlight  is  made  up  of 
simple  components  corresponding  to  oscillations  ranging 
all  the  way  from  about  370  billions  to  about  900  billions 
per  second.  The  quality  of  the  simple  color-sensations 
discovered  by  this  analysis  varies  characteristically  —  as 
the  following  table  will  help  to  illustrate  —  according  to 
the  changes  in  number  of  the  oscillations. 


NAME  OF  FRAUNHOFER'S  LINE. 

NUMBER  OF  VIBRA- 
TIONS PER  SECOND. 

W  AYE  -LENGTHS  IN  THE  AIR. 

B   ........ 

Billions. 

450 

Millimeters. 

0.000  6878 

c  

472 

0  000  6564 

D  .    . 

526 

0.000  5888 

E  

589 

0.000  5260 

F  

640 

0  000  4843 

G  

722 

0  000  4291 

H 

790 

0  000  3928 

The  table  shows  that  rays  of  light  which  have  a  number 
of  oscillations  less  than  450  billions  per  second,  so  far  as 
they  affect  the  retina  at  all,  occasion  the  sensation  of  red. 
This  sensation  does  not  change  quality  greatly  as  the 
number  of  oscillations  rises  from  450  to  470  billions. 
Beyond  this  limit  ((7),  however,  the  quality  of  the  color- 
sensation  changes  rapidly,  takes  on  a  yellowish  tone 
(orange),  and  finally  at  526  billions  (Z>)  corresponds  to  a 
decided  yellow.  This  sensation  then  becomes  greenish,  as 
the  number  of  oscillations  increases,  until  they  reach  about 
589  billions  per  second,  when  green  (J£)  appears.  The 
green  then  becomes  bluish,  and  at  640  billions  blue  (^) 
begins  to  arise.  From  this  on  to  about  722  billions  (17- Gr) 


258  PHYSIOLOGICAL  PSYCHOLOGY. 

the  colors  lie  between  the  blue  and  the  violet  until  the 
decided  violet  comes  to  view. 

The  spectrum  has  no  sharply  denned  limit  at  either  end. 
At  both  ends  it  passes  gradually  into  black,  but  more 
gradually  at  the  violet  than  at  the  red  end. 

Brightness  of  Color-tones.  —  The  impression  made  by  the 
colors  lying  immediately  about  D  (D-E)  is  stronger  than 
elsewhere.  Or,  as  we  should  say,  the  colors  are  naturally 
"  brighter  "  here  (about  the  green-yellow  of  the  spectrum) 
than  the  other  colors.  This  difference  cannot  be  due  to 
the  objective  energy  of  the  rays  of  light,  whether  as 
measured  by  their  chemical  or  their  calorific  effect.  It 
must  be  due,  then,  to  the  structure  of  the  retina,  and  its 
peculiar  sensitiveness  to  stimulations  by  the  color-rays  of 
this  region  of  the  spectrum.  Crimson  light  requires  many 
times  more  energy  than  green  in  order  to  be  strong  enough 
to  read  by  it. 

Least  Perceptible  Variations  of  Colors.  —  The  sensitiveness 
of  the  retina  to  slight  variations  in  quality  of  the  color- 
tones  is  also  different  at  different  portions  of  the  spectrum. 
In  general,  it  is  greatest  in  the  blue  and  blue-green  regions 
(D  and  F).  The  precise  ratios  which  express  this  differ- 
ence of  sensitiveness  to  slight  variations  at  different  por- 
tions of  the  spectrum  are  given  somewhat  differently  by 
different  observers. 

The  Composite  Nature  of  Colors.  —  Our  ordinary  color- 
sensations,  like  those  of  musical  sounds,  are  not  pure  and 
simple,  but  complex.  For  the  analysis  of  these  sensations, 
however,  unlike  that  of  musical  sounds,  the  method  of 
conscious  discrimination  is  of  no  avail.  Sensations  of  color 
cannot  be  mentally  analyzed  into  their  constituent  elements. 
They  persistently  maintain,  in  consciousness,  that  single 
and  uncompounded  quality  which  has  resulted  from  the 
fusion  of  the  different  elements  supplied  by  the  rays  of 
different  color-tone. 


QUALITY   OF    SENSATIONSo  259 

When  the  wave-lengths  of  the  two  colors  that  are  mixed 
vary  but  slightly  from  each  other  (a  few  billion  oscillations 
per  second),  the  result  of  their  mixture  may  be  recognized 
as  a  "  shade  "  of  one  of  the  same  two  colors.  Thus  many 
shades  of  so-called  "  orange  "  would  readily  be  recognized 
as  mixtures  of  yellow  and  red.  That  certain  blues  are 
greenish,  or  greens  bluish,  is  manifest  to  everybody. 

The  color-impressions  formed  by  mixture  are  not  all 
different  from  each  other.  So  that  if  we  were  to  mix  color- 
tones  that  lie  apart  at  all  possible  distances  along  the 
spectrum,  the  number  of  resulting  compounds  would  not 
be  unlimited.  In  fact,  the  number  of  the  resulting  sensa- 
tions would  be  much  less  than  the  number  of  the  compound 
physical  processes  which  stimulate  the  retina.  The  quality 
of  these  colors  formed  by  mixture  depends  upon  the  place 
in  the  spectrum  from  which  the  simple  color-tones  are 
selected,  and  upon  their  intensity.  Moreover,  we  may 
discover  two  ways  of  advancing,  by  this  process  of  mixing 
color-tones,  to  any  of  the  composite  colors.  We  may  pass, 
for  example,  from  yellow  to  blue,  either  through  green- 
yellow,  green,  and  blue-green,  or  through  orange,  red, 
purple,  and  violet. 

Number  of  Colors  Distinguishable,  —  Newton  formed  a  sort 
of  octave  of  fundamental  colors,  consisting  of  the  seven 
members, — red,  orange,  yellow,  green,  blue,  indigo,  and 
violet.-  But  there  is  really  no  basis  for  this  classification, 
either  in  science  or  in  ordinary  experience  and  usage. 
Indigo,  as  a  kind  of  semi-tone  between  blue  and  violet,  has 
no  more  right  to  a  place  in  this  scale  than  have  many  other 
intermediate  tones  ;  the  same  is  substantially  true  of  orange. 
The  purples,  which  lie  on  the  scale  between  the  blues  and 
the  reds,  are  entirely  overlooked  in  this  classification ;  the 
browns,  too,  find  no  place  anywhere. 

Before  raising  the  question  as  to  how  few  in  number  are 
the  colors  which  may  be  called  "  fundamental,"  we  may  fitly 


260 


PHYSIOLOGICAL   PSYCHOLOGY. 


notice  that  the  number  of  color-tones  actually  discernible 
by  the  human  eye  is  very  great.  One  authority  places  it, 
in  oil-colors,  at  100  ;  but  in  the  spectrum  another  authority 
thinks  it  possible  to  discover  230  distinct  tints.  Herschel 
considered  that  the  workers  on  the  mosaics  at  Rome  must 
have  distinguished  30,000  different  color-tones.  If  we 
allow  for  differences  of  brightness  and  purity  of  tone,  the 
actual  number  of  sensations  possible  with  this  sense,  may 
well  reach  into  the  hundreds  of  thousands. 

Complementary  Colors.  —  If  certain  color-tones,  having  a 
given  intensity,  are  united  on  the  retina,  the  result  is  a 
sensation  wholly  unlike  either  of  the  two  thus  united. 
This  sensation  we  call  "  white  "  ;  and  the  two  colors  which 
produce  it  by  their  admixture  are  called  "  complementary." 
Such  a  mixture  may  be  obtained  in  various  ways,  —  e.g.  by 
superimposing  two  spectral  rays,  by  blending  the  reflected 
images  of  two  colored  wafers,  or  the  visual  impressions  of 
colored  surfaces  on  a  revolving  top  or  wheel,  etc. 

Following  is  Helmholtz's  table  of  complementary  colors : 


COLOR. 

WAVE-LENGTH. 

COMPLEMENTARY 
COLOR. 

WAVE-LENGTH. 

RELATION  OF 
WAVE-LENGTH. 

Red 

2,425 

Green-blue 

1,818 

1,334 

Orange 

2,244 

Blue 

1,809 

1,240 

Gold-yellow 

2,162 

Blue 

1,793 

1,206 

Gold-yellow 

2,120 

Blue 

1,781 

1,190 

YeUow 

2,095 

Indigo-blue 

1,716 

1,221 

Yellow 

2,085 

Indigo-blue 

1,706 

1,222 

Green-yellow 

2,082 

Violet 

1,600 

1,301 

The  complementary  colors  for  different  persons  are  not 
always  precisely  the  same  ;  indeed,  they  may  differ  for  the 
two  eyes  of  the  same  person. 

duality  as  related  to  Intensity.  —  When  the  intensity  of 
the  light  approaches  either  a  maximum  or  a  minimum, 


.     QUALITY   OF   SENSATIONS.  261 

important  changes  in  the  quality  of  the  resulting  sensa- 
tion occur  which  are  independent  of  changes  in  the  wave- 
length. At  the  maximum  intensities  all  distinctions  of 
color-tone  cease,  and  even  homogeneous  rays  appear  white. 
Before  reaching  this  maximum,  red  and  green  pass  over 
into  yellow.  Near  the  minimum  intensities  every  color- 
tone,  except  "  saturated  "  red,  becomes  colorless  when  seen 
alone  on  a  perfectly  black  ground.  The  different  color- 
tones  disappear  at  different  degrees  of  intensity  of  the 
light,  —  green  remaining  visible  in  the  weakest  light. 

Quality  as  related  to  Time.  —  Changes  of  color-tone  take 
place  when  the  time  during  which  the  light  acts  upon  the 
retina  is  reduced  to  a  minimum.  A  certain  "  light-mass  " 
(considered  as  the  product  of  duration  by  intensity')  is  nec- 
essary for  a  sensation  of  light  or  color.  Sensations  of 
saturated  color  can  be  produced  by  instantaneous  illumi- 
nation of  the  spectrum  with  an  electric  spark ;  but  more 
time  is  needed  to  produce  these  sensations  with  a  weaker 
light. 

On  this  subject  a  recent  investigator  has  arrived  at  the 
following  conclusions :  (1)  As  the  illumination  increases, 
the  rate  of  the  waning  of  the  sensation  decreases.  (2)  For 
weak  illuminations  and  brief  stimulations,  the  waning 
of  the  sensation  is  nearly  inversely  as  the  square  of  the 
illumination.  (3)  The  color  of  the  light  has  no  effect. 
[This  point  is,  however,  disputed  by  other  observers.] 
(4)  Exposure  of  the  eye  to  a  dark  room  increases  the  sen- 
sation. 

Quality  as  related  to  Zones  of  the  Retina.  —  Important 
changes  -in  the  quality  of  our  sensations  of  light  and  color 
are  dependent  upon  the  place  of  the  retina  on  which  the 
stimulus  falls.  For  purposes  of  experiment  the  entire 
organ  has  sometimes  been  divided  into  three  zones,  —  a 
central  or  polar,  a  middle,  and  an  outer  or  peripheral. 
These  regions  seem  to  differ  as  respects  the  distinctness, 


262  PHYSIOLOGICAL   PSYCHOLOGY. 

the  quality,  and  the  intensity,  of  the  sensations  produced 
by  the  same  stimulus.  In  general,  while  an  indefinite 
number  of  clearly  distinguishable  color-tones  are  possible 
when  the  light  falls  on  the  polar  zone,  this  number  is 
reduced  to  comparatively  few  impressions  on  the  middle 
zone ;  and  all  color-tones  gradually  become  indistinguish- 
able on  passing  through  the  outer  zone.  At  a  certain 
distance  from  the  centre,  blue  and  yellow  alone  are  seen ; 
and  farther  away,  none  of  the  color-tones  are  apparent. 
Red  changes  through  orange  and  violet  to  blue,  as  we  pass 
toward  the  periphery  of  the  retina.  Blue  and  yellow 
become  paler, — apparently  in  proportion  to  the  amount  of 
green  in  them. 

The  best  evidence  seems  to  show  that  the  sensitiveness 
of  the  retina  to  sensations  of  light  —  unlike  that  of  color- 
tones  —  increases  toward  the  peripheral  region.  The 
opposite  of  this  view  has,  however,  been  maintained. 
Recent  and  apparently  careful  experiments  fix  the  maxi- 
mum sensitiveness  to  light  at  a  distance  of  20°-25°  hori- 
zontal, and  12°-15°  vertical,  from  the  retinal  centre.  The 
lower  portion  is  found  to  be  less  sensitive  than  the  upper ; 
and  possibly  the  temporal  side  is  more  sensitive  than  the 
other  side  of  the  retinal  area.  The  cause  of  this  increase 
in  sensitiveness  toward  the  periphery  is  unknown.  It  has 
been  conjectured  that  this  is  due  to  the  highly  developed 
structure  of  the  rods  which  act  as  mirrors  to  reflect  the 
light. 

Phenomena  of  Color-blindness.  —  In  certain  cases,  defects 
of  vision  exist  which  seem  to  show  that  the  entire  retina  of 
some  individuals  resembles  the  middle  or  the  outer  zone 
of  the  normal  retina.  Such  individuals  are  said  to  be 
"color-blind."  Two  classes  of  cases  are  distinguished. 
In  the  one  class,  which  is  much  the  more  frequent,  a  par- 
tial or  complete  insensitiveness  to  red  rays  exists;  the 
spectrum  may  then  be  said  to  be  shortened  at  the  red  end. 


QUALITY   OF   SENSATIONS.  263 

In  other  cases  this  insensitiveness  applies  also  to  the  green 
or  blue-green  or  green-yellow  or  "  blue-violet  "  color-tones. 
It  has  been  proposed  to  divide  all  cases  of  color-blindness 
into  two. groups,  —  the  "red-blind"  and  the  "  green-blind." 

Important  modifications  of  the  sensations  of  light  and 
color  are  due  to  the  previous  condition  of  the  retina,  or  to 
the  contemporaneous  condition  of  the  parts  adjoining  that 
on  which  the  stimulus  falls.  Under  the  first  head  fall  the 
phenomena  of  "inertia"  and  "exhaustion";  under  the 
second,  the  phenomena  of  "  contrast."  In  both  classes  of 
cases  there  is  some  evidence  to  show  that  obscure  complica- 
tions, of  a  cerebral  rather  than  a  peripheral  origin,  have  an 
influence  on  the  result.  This  should  be  borne  in  mind  in 
considering  those  relations  of  quality,  and  its  changes, 
which  are  now  to  be  examined. 

Phenomena  of  After-images.  —  If  we  close  our  eyes  after 
looking  for  a  time  intently  at  any  bright  object,  an  image 
of  this  object  remains  for  some  time  and  only  gradually 
fades  out  of  sight.  Such  an  image  is  called  a  "positive 
after-image,"  because  its  bright  and  dark  parts  correspond 
to  those  of  the  original  object.  This  delay  in  the  fading 
away  of  the  image  from  the  retina  is  said  to  be  due  to  the 
physiological  "  inertia  "  of  the  organ. 

But  if  we  continue  to  regard  the  after-image,  we  observe 
that  its  parts  undergo  a  change  of  color.  The  white 
changes  into  greenish  blue  ;  then  into  indigo-blue,  violet, 
and  finally  a  deep  rose  color.  If  we  look  at  a  green  sur- 
face for  some  time,  and  then  fix  the  eye  upon  a  white 
surface,  the  latter  will  become  of  a  red  color.  In  general, 
the  color  which  this  class  of  after-images  assumes  is  the 
color  "  complementary  "  of  the  color  of  the  object.  These 
images  are  therefore  called  "  negative  after-images."  More- 
over, the  color-tones  of  the  spectrum  can  be  made  to 
appear  brighter  by  looking  at  them  immediately  after 
having  filled  the  eye  for  some  time  with  the  complemen 


264  PHYSIOLOGICAL   PSYCHOLOGY. 

tary  color.  It  thus  appears  that  some  spectral  colors  are 
not  completely  "saturated."  Such  phenomena  are  said 
to  be  due  to  the  principle  of  "  exhaustion."  The  end- 
organs  —  and  also,  it  is  probable,  the  central  organs  —  after 
use  upon  one  color-tone,  for  a  time  lose  their  sensitiveness 
to  the  stimulus  which  produces  this  color-tone. 

Phenomena  of  Contrast.  —  A  bright  object  appears  brighter 
with  surroundings  darker  than  itself,  and  darker,  with  sur- 
roundings brighter  than  itself.  In  the  case  of  gray  disks 
on  a  background  darker  than  themselves,  the  increase  of 
brightness  is  found  to  be  closely  proportional  to  .the  differ- 
ence in  brightness  between  the  disk  itself  and  the  back- 
ground; but  it  is  probably  independent  of  the  absolute 
brightness  of  the  latter.  This  phenomenon  is  called  "  con- 
trast,"—  the  word  in  this  instance  being  applied  to 
brightness  of  color-tone. 

When  colored  instead  of  white  light  is  used  in  exper- 
imenting under  this  law,  phenomena  similar  to  those  of 
complementary  colors  are  obtained.  For  example,  a  small 
square  of  white  on  a  surface  of  green,  when  covered  with 
a  transparent  sheet  of  tissue-paper,  appears  as  red  on  a 
surrounding  surface  of  a  whitish  hue  ;  on  a  red  ground  it 
appears  as  green,  on  a  blue  ground  as  yellow,  and  on  a 
yellow  ground  as  blue. 

As  yet  we  have  no  full  and  satisfactory  explanation  of 
the  phenomena  of  contrast.  Helmholtz  at  one  time  ascribed 
it  to  deceptions  of  judgment,  such  as  we  are  familiar  with 
in  estimating  distances.  But  this  theory  seems  strained 
and  remote  from  the  facts.  A  satisfactory  partial  explana- 
tion is  found  in  the  physiological  principle  that  stimulus 
of  any  element  of  the  retina  tends  to  spread  over  contig- 
uous elements ;  and,  in  turn,  the  effect  of  the  stimulus  on 
the  elements  on  which  it  falls  is  modified  by  the  condition 
of  the  contiguous  elements.  But  besides  all  this,  we  seem 
compelled  to  refer  to  the  influence  of  obscure  cerebral 


QUALITY   OF   SENSATIONS.  265 

conditions  that  are  dependent  upon  the  associated  action 
of  the  nervous  elements  of  the  cerebral  centres  themselves. 
The  necessity  for  this  will  be  more  apparent  when  we 
come  to  consider  the  formation  of  visual  perceptions. 

GENERAL   THEORY  OF   VISUAL  SENSATIONS. 

The  complicated  character  of  the  sensations  of  light  and 
color,  as  respects  their  quality,  renders  it  peculiarly  diffi- 
cult to  frame  any  general  theory  which  shall  embrace  and 
satisfy  all  the  phenomena.  The  groups  of  facts,  which 
chiefly  need  theoretical  explanation,  are  the  following: 

(1)  It  is  possible  to  produce  all  the  color-tones  by  mixing 
certain  fundamental  colors,  which  must  be  at  least  three 
(and  probably,  better,  four)  in  number.     And  the  inter- 
mediate shades  lying  between  any  two  proximate  color- 
tones   can   be   produced    by   mingling    these   color-tones. 

(2)  The  saturation  or  purity  of  the  color-tones  depends 
upon  the  intensity  of  the  light;  and  all  the  color-tones 
may  be  graded  downward,  as  it  were,  into  colorless  light. 

(3)  Any  two   colors  of   the  spectrum  chosen  at   proper 
intervals  along  its  scale,  when  mixed,  will  produce  white. 

(4)  The   theory  must  explain   the   phenomena   of  after- 
images, color-blindness,  and  contrast,  either  by  the  way  in 
which  it  regards  the  preceding  classes  of  facts,  or  in  some 
secondary  manner  derived  from,  and  based  upon,  these 
facts. 

Yoimg-Helmholtz  Theory  of  Visual  Sensations,  —  Among 
the  several  theories  proposed  for  the  explanation  of  the 
foregoing  phenomena,  that  brought  forward  by  Young 
and  elaborated  by  Helmholtz  has  been  most  widely  ac- 
cepted. This  theory  takes  its  point  of  starting  from  the 
fact  that  we  can  produce  all  the  many  color-tones  by  mix- 
ture of  a  few  so-called  "fundamental  "  colors.  It  assumes 
three  fundamental  colors.  Of  these,  green  must  be  one, 
because  green  has  no  complementary  color.  The  other 


PHYSIOLOGICAL  PSYCHOLOGY. 


two  may  then  be  taken  from  the  two  ends  of  the  spectrum ; 
they  are  red  and  either  violet,  or  indigo,  or  blue. 

It  is  then  further  assumed  that,  in  every  sensitive  por- 
tion of  the  retina,  three  kinds  of  nervous  elements  exist. 
The  excitation  of  each  of  these  elements  separately  would 
produce  only  that  kind  of  fundamental  color-tone  which  is 
peculiar  to  the  specific  elements  excited.  We  may  say, 
then,  that  there  are  in  the  retina  elements  of  "  green-color 
sensation,"  elements  of  "  red-color  sensation,"  and  elements 
of  "  blue-color  sensation." 

But  every  actual  sensation  is  a  complex  affair.  Its  char- 
acter is  determined  by  the  relative  intensities  with  which 
the  different  kinds  of  nervous  elements  are  combined  to 
produce  it.  This  may  be  illustrated  by  the  accompanying 
diagram  (No.  76),  where  the  curved  lines  R,  Gr,  and  B 


G    H 


FIG.  76.— Diagram  from  Fick,  illustrating  the  Young-Helmholtz  Theory.     (For  ex- 
planation, see  the  text.) 

represent  the  three  fundamental  colors,  and  the  curves 
described  by  them  show  the  strength  of  the  influence  exer- 
cised by  these  colors  in  forming  the  complex  result ;  while 
the  perpendicular  lines  indicate  the  several  color-tones  of 
the  spectrum. 

The  Young-Helmholtz  Theory  should  be  gratefully  rec- 
ognized as  a  brilliant  attempt  at  explaining  the  phenom- 


QUALITY   OF   SENSATIONS.  267 

ena  of  sensations  of  light  and  color.  It  is  most  success- 
ful with  the  facts  that  relate  to  the  mixing  of  colors. 
It  is  perhaps  most  unsuccessful  with  the  phenomena  of 
color-blindness,  contrast,  and  the  dependence  of  color- 
tones  on  time,  place  of  the  retina  stimulated,  etc.  Those 
who  dispute  it  consider,  and  apparently  with  good  reason, 
that  its  failure  on  these  points  is  decisive  against  it.  For 
example,  it  does  not  appear  that  the  colors  wanting  in  the 
different  forms  of  color-blindness  correspond  to  the  three 
fundamental  colors  of  the  normal  system.  Red-blind  per- 
sons ought,  according  to  this  theory,  to  see  white  as  green- 
ish blue,  and  green-blind  persons  ought  to  see  it  as  purple. 
But  apparently  both  see  white  as  we  all  do.  Moreover, 
pure  yellow  is  not  displaced,  in  the  spectrum  of  the  color- 
blind, in  the  direction  of  green,  or  pure  blue  in  the  direction 
of  violet. 

It  must  be  confessed  that  the  more  elaborate  theories 
which  have  been  proposed  to  take  the  place  of  that  known 
by  the  name  "  Young-Helmholtz  "  are  scarcely  more  satis- 
factory. We  shall  refer,  however,  to  one  or  two  of  them. 

Bering's  Theory  of  Visual  Sensations.  —  This  authority 
insists  that  we  must  regard  the  changes  of  sensation 
through  which  we  pass  when  viewing  the  different  shades 
of  gray,  from  white  to  black,  as  analogous  to  other  color- 
sensations.  Moreover,  he  considers  that  six,  instead  of 
three,  color-tones  must  be  assumed  as  fundamental,  in  order 
to  produce  all  the  other  color-tones  by  admixture  of  these 
six.  Hering,  therefore,  proposes  the  following  pairs  of 
fundamental  color-tones,  —  black  and  white,  green  and 
red,  blue  and  yellow.  The  first  member  of  each  pair 
(black,  green,  and  blue)  he  considers  to  be  the  result  of 
a  process  of  "  construction "  of  visual  substance.  The 
second  member  of  each  pair  (white,  red,  and  yellow)  he 
ascribes  to  the  "  destruction  "  of  such  visual  substance. 

Apparently  decisive  objections  to  this  theory  have  been 


268  PHYSIOLOGICAL   PSYCHOLOGY. 

brought  forward.  Among  them  one  of  the  most  conclusive 
seems  to  be  the  following.  A  light  composed  of  red  and 
green  may  be  made  to  seem  to  the  eye  the  same  as  a 
light  composed  of  yellow  and  blue.  If,  then,  the  eye  is 
"fatigued"  to  red,  instead  of  the  red-green  mixture  ap- 
pearing greenish,  and  so  distinguishable  from  the  yellow- 
blue  mixture,  they  both  appear  the  same  to  the  fatigued 
eye. 

Wundt's  Theory  of  Visual  Sensations.  —  Another  view  em- 
phasizes a  supposed  difference  in  the  processes,  rather  than 
in  the  kinds  of  retinal  elements,  belonging  to  the  different 
color-tones.  A  very  elaborate  example  of  such  a  view  is 
the  theory  of  Wundt.  We  state  only  a  few  of  its  principal 
features.  (1)  The  retina  may  be  assumed  to  be  in  a  con- 
stant state  of  internal  excitation,  to  which  the  sensation 
of  black  corresponds.  Hence  when  other  excitations  are 
absent,  we  have  the  sensations  of  more  or  less  darkness. 
(2)  Every  external  excitation  sets  up  two  kinds  of  processes 
in  the  retina,  —  one  a  color  process  ("chromatic"),  the 
other  a  colorless  process  ("achromatic").  These  two 
processes  follow  different  laws.  (3)  The  colorless  (achro- 
matic) process  is  of  a  uniform  photochemical  character; 
and  its  intensity  in  uni-colored  light  is  dependent  partly 
on  the  intensity  of  the  light,  and  partly  on  the  length  of 
the  waves.  It  reaches  a  maximum  at  yellow,  and  falls  off 
in  both  directions.  (4)  The  color  (chromatic)  process  is 
of  a  manifold  photochemical  character,  and  it  changes  by 
insensible  degrees  with  the  length  of  the  wave.  (5)  Each 
process  of  excitation  outlasts  for  a  certain  time  the  stim- 
ulus which  occasions  it,  and  exhausts  the  sensibility  of  the 
sensory  substance  for  the  stimulus. 

By  combining  these  features,  Wundt  thinks  that  all  the 
phenomena,  except  those  of  contrast,  which  are  due  to  a 
cerebral  origin,  may  be  accounted  for. 

Symbolism  of  Visual  Sensations.  —  The  foregoing  laws  of 


QUALITY   OF   SENSATIONS. 


269 


the  changes  in  visual  sensations,  and  the  nature  of  the 
theory  which  must  be  devised  to  account  for  them,  have 
been  represented  to  the  eye  by  various  ingenious  devices. 
Among  them  the  most  common  is  the  so-called  color  tri- 


FIG.  77.  —Color-triangle,  from  Fick.     (For  explanation,  see  text.) 

angle  (see  Fig.  77).  In  this  triangle  the  different  color- 
tones  may  be  regarded  as  lying  along  a  curved  line,  from 
red  to  violet ;  and  the  difference,  in  the^scale,  between  any 
two  color-tones  is  measured  by  the  angle  made  by  two  lines 
drawn  from  the  point  W  through  the  points  occupied  on 
the  lines  by  those  two  color-tones. 


270 


PHYSIOLOGICAL   PSYCHOLOGY. 


Figure  78  is  a  scheme  for  showing  the  relations  of  color- 

tones  by  two  concentric  circles, 
each  color  in  one  circle  corre- 
sponding to  its  complementary 
color  in  the  other  circle.  In 
the  phenomena  of  contrast,  if 
the  color  inducing  the  contrast 
be  represented  by  a  segment 
of  the  inner  circle,  the  coinci- 
dent segments  of  the  two  cir- 
cles represent  the  direction  in 

whi°h    tLe    induCed    change    is 
For  example,  the  S6g- 

ments  representing  green  and  purple  coincide,  and  so  do 
those  representing  red  and  blue-green.  Green  on  a  red 
ground  is,  therefore,  modified  as  it  would  be  if  blue-green 
were  mixed  with  it;  and  red  on  a  green  ground,  as  it 
would  be  if  purple  were  mixed  with  it. 


PCS.  78.  -Scheme   for  showing  the 
Relations  of  Color-tone  (see  text).  moving 


CHAPTER  XII. 

THE   QUANTITY  OF  SENSATIONS. 

BY  an  act  of  mental  analysis,  which  all  can  perform,  the 
amount  of  sensations  is  distinguished  from  their  kind,  the 
intensity  from  the  quality.  The  nature  of  this  analysis 
may  be  illustrated  by  familiar  examples :  such  are  the 
"  dying  away "  of  the  tone  when  a  skilful  player  draws 
his  bow  with  gradually  diminishing  force  over  the  string 
of  a  violin  ;  or  the  increase  in  the  noise  made  by  a  bell  as 
we  approach  the  place  where  it  is  sounding.  So,  too,  we 
readily  recognize  changes  in  our  sensations  when  more  of 
pressure  or  of  temperature,  whether  hot  or  cold,  is  applied 
to  the  skin. 

Ordinary  Experience  Insufficient.  —  It  is  also  obvious,  how- 
ever, that  the  measurement  of  the  amount  of  our  sensations 
by  consciousness  directly,  is  very  inexact.  This  is  true 
even  when  the  sensations  compared  belong  to  the  same 
sense.  We  should  hesitate,  for  example,  to  say  whether  a 
given  noise  were  four,  or  five,  times  as  loud  as  one  imme- 
diately preceding.  And  no  one  would  think  of  affirming 
the  exact  fraction,  in  hundredths,  of  the  amount  by  which 
the  brilliancy  of  one  lamp  surpasses  that  of  another. 

The  inadequacy  of  such  direct  comparison  of  sensations 
in  consciousness  becomes  more  apparent  when  we  attempt 
to  place  sensations  of  the  different  senses  side  by  side. 
We  apply,  indeed,  terms  of  intensity  —  such^as  "weak," 
"very  weak,"  "strong,"  "very  strong,"  or  "moderate," 
etc.  —  to  all  kinds  of  sensations.  But  we  should  consider 
it  absurd  to  affirm :  The  rose  smells  as  sweet  as  the  grass 
looks  green ;  or,  The  coffee  is  as  strong  as  the  sky  is  blue. 

271 


272  PHYSIOLOGICAL  PSYCHOLOGY. 

That  the  measurement  of  the  quantity  of  our  sensations 
is  complicated  with  changes  in  their  characteristic  quality 
has  already  been  remarked.  Increase  in  the  brightness  of 
a  color  invariably  changes  its  characteristic  color-tone. 
The  strong  smell  of  musk  or  assafoetida  is  not  the  same 
kind  of  sensation  as  the  weak  smell  of  these  objects.  Only 
in  the  case  of  musical  tones  are  we  able  at  the  same  time 
carefully  to  attend  to  both  the  quantity  and  the  quality  of 
our  sensations,  and  so  approximately  determine  that  the 
former  is  changing  while  the  latter  remains  unchanged. 
Even  in  the  case  of  these  acoustic  sensations,  any  consid- 
erable change  of  intensity  changes  also  the  relation  of  the 
over-tones  to  the  fundamental  tone,  and  so  the  "  tone-color- 
ing "  of  the  "  clang." 

Two  Questions  relating  to  Quantity.  —  The  general  inquiry 
into  the  quantity  of  our  sensations  involves  two  subordi- 
nate questions.  These  are  :  (1)  How  little,  or  how  much, 
respectively,  of  each  kind  of  stimulus  produces  the  least,  or 
the  greatest,  amount  of  resulting  sensation,  of  which  the 
mind  is  capable  ?  and  (2)  What  is  the  law  regulating  the 
relation  in  which  changes  in  the  intensity  of  sensations,  as 
estimated  in  consciousness,  depend  upon  changes  in  the 
intensity  of  the  external  stimuli?  The  first  question  is 
a  question  of  the  limits  within  which  sensations  may  vary 
in  quantity  and  remain  sensations  of  the  same  sense.  The 
second  question  is  a  question  of  the  uniform  relations  (or 
law)  which  are  maintained,  within  the  limits,  among  the 
various  sensations  compared. 

Difficulties  of  the  Investigation.  —  The  answer  to  both  of 
the  foregoing  questions  is  accompanied  by  many  difficul- 
ties. It  has  just  been  shown  that  our  subjective  standards 
for  measuring  the  amounts  of  our  sensation-experience  are 
very  inadequate.  The  objective  standards  for  measuring 
the  quantities  of  the  stimuli  which  occasion  the  sensations 
are  also  far  from  satisfactory.  This  is,  of  course,  especially 


QUANTITY   OF   SENSATIONS.  273 

true  of  the  senses  of  taste  and  smell ;  since  we  do  not  even 
know  what  properties  smellable  and  tastable  substances 
must  possess  in  order  to  irritate  the  nerves  of  these  senses. 
So  is  the  measurement  of  the  stimulus  which  occasions 
sensations  of  temperature  made  difficult  by  the  fact  that 
its  amount  is  dependent  upon  the  zero-point  of  the  skin 
itself, — a  matter  that  varies  greatly  and  is  always  difficult 
of  determination.  For  sensations  of  pressure,  light,  and 
sound,  we  can  make  the  necessary  determinations  with  a 
greater  approach  to  exactness. 

The  "  Least  Observable  Difference."  —  There  is,  however, 
one  kind  of  measurement  respecting  the  quantity  of  sen- 
sation which  can  be  made  in  consciousness  with  a  great 
degree  of  accuracy.  Suppose  that  two  sensations  of  the 
same  quality  are  produced,  either  in  quick  succession  upon 
the  same  area  of  the  organ  of  sense,  or  simultaneously 
upon  corresponding  areas  of  the  organ,  by  amounts  of 
stimuli  that  are  equal,  or  very  nearly  equal:  then  the 
attentive  mind  can  tell  with  considerable  accuracy  whether 
the  intensities  of  the  two  sensations  are  exactly  equal,  or 
differ  minutely.  This  difference  of  quantity  in  the  sensa- 
tions which  marks  the  limits  of  the  mind's  power  of  dis- 
cernment is  called  "  the  least  observable  difference."  The 
problem  of  measuring  accurately  the  quantity  of  sensations 
becomes  then  the  problem  of  determining  the  least  observable 
difference  of  quantity  for  each  kind  of  sensations,  and  for 
every  point  along  the  scale  of  degrees  of  quantity. 

[Much  debate  has  arisen  over  the  question  :  Is  the  least 
observable  difference  of  two  sensations  itself  a  constant 
quantity  ?  Into  the  nature  and  merits  of  this  debate  we 
cannot  undertake  to  enter.  In  the  way  in  which  the  ques- 
tion is  often  discussed,  the  whole  matter  is,  in  our  judg- 
ment, resolved  into  misleading  figures  of  speech.  There 
is  no  mental  entity,  or  mental  state,  corresponding  to  this 
term,  "  least  observable  difference." 


274  PHYSIOLOGICAL  PSYCHOLOGY. 

For  example,  if  the  additon  of  n  to  the  stimulus  S  is 
the  smallest  amount  that  will  so  change  the  mental  state 
x  as  to  make  it  pass  over  into  a  state  x\  —  which  latter 
state  the  mind  judges  to  be  a  state  of  increased  amount 
of  sensation,  —  then  we  can  recognize  and  accept  this  fact 
as  a  fact.  It  does  not  follow,  however,  that  we  may  argue 
that  x'— o;  =  A,  and  that  this  A  is  itself  entitled  to  be 
called  a  "  least  observable  difference,"  as  though  it  were  a 
fixed  quantity  of  mental  experience.  There  are  in  con- 
sciousness the  sensations  x  and  x' ;  and  we  judge  one  to  be 
greater  than  the  other.  But  A  (or  x'  —  x)  is  only  a  fiction 
growing  out  of  a  figurative  application  of  mathematical 
terms  to  subjects  that  elude  all  correct  representation  by 
such  terms.] 

Methods  of  determining  the  Limits.  —  There  are  two  ways 
of  determining  the  lower  limit,  or  least  amount  of  stimulus 
which  occasions  any  sensation  at  all.  We  may  choose  a 
weak  stimulus,  that  is,  however,  slightly  stronger  than  is 
necessary  to  produce  a  sensation  when  applied;  and  we 
may  then  diminish  it  by  minute  gradations  until  the 
exact  point  is  reached  and  noted  at  which  it  ceases  to 
produce  any  sensation  at  all.  Or,  we  may  choose,  at  first, 
a  stimulus  too  weak  to  produce  any  sensation,  and  then 
increase  it  by  gradual  minute  increments  until  the  point  is 
reached,  and  noted,  at  which  some  sensation  is  produced. 
By  these  two  methods  the  "  sensitiveness  "  of  the  different 
areas  of  the  different  organs,  under  different  circumstances, 
may  be  tested. 

In  the  cases  of  sight  and  sound  the  attempt  to  fix  the 
lower  limits  of  the  sensations  is  greatly  embarrassed  by 
the  fact  that  the  organs  of  sensation  are  rarely  or  never 
perfectly  free  from  excitation  beyond  our  control.  The 
eye  has  its  "  own-light ";  the  ear  is  never  in  "  absolute 
stillness,"  or  freedom  from  stimulus  by  the  movements  of 
surrounding  structures  of  the  head. 


QUANTITY   OF   SENSATIONS.  275 

The  upper  limit,  or  maximum  amount  of  stimulus  which 
results  in  producing  sensations  of  each  class,  cannot  be 
determined  experimentally.  Large  quantities  of  stimulus 
not  only  fatigue  and  endanger  the  nervous  structure  upon 
which  they  act ;  but  they  also  arouse  such  an  amount  of 
painful  feeling,  and  of  influence  from  allied  forms  of  sensa- 
tion, as  to  overwhelm  the  particular  kind  of  sensation 
whose  quantity  it  is  desired  to  measure.  Very  concen- 
trated odors  or  solutions,  exceedingly  intense  lights  and 
noises,  are  not  simply  smelled,  or  tasted,  or  seen,  or  heard ; 
they  are  all  painfully  felt,  as  it  were,  over  extended  areas 
of  the  bqdy. 

We  may  affirm  in  general, however,  that  the  "capacity" 
of  each  sense  varies  directly  as  the  amount  of  stimulus 

which  it  can  receive.     Let  —  stand  for  the  measure  of  the 

S 

sensitiveness  of  the  sense,  and  C  stand  for  the  measure  of 

C 
its  capacity ;  then  —  will  represent  the  "  circuit "  or  range 

o 

of  the  sensations  of  which  the  sense  is  capable. 

Methods  of  determining  the  Least  Observable  Difference.  — 
There  are  three  different  ways  of  measuring  the  sensitive- 
ness of  the  mind  to  minute  changes  in  the  amount  of  sen- 
sations as  dependent  upon  changes  in  the  intensity  of  the 
stimuli.  Of  these  the  first  (1)  is  called  "  the  method  of 
least  observable  difference."  Two  ways  of  applying  the 
principle  of  this  method  are  to  be  noticed.  If  we  follow 
one  of  these  ways  (sometimes  called  "  the  method  of  mean 
gradations  "),  we  first  select  two  sensations,  produced  by 
two  different  intensities  of  the  stimulus,  which  are  sepa- 
rated by  a  clearly  perceptible  interval  as  respects  their 
quantity  ( A  and  0),  and  we  then  inquire,  what  intensity  of 
the  stimulus  is  necessary  to  produce  a  sensation  that  seems 
to  lie  exactly  midway  (M )  between  these  two  ?  In  other 
words,  we  try  to  locate  the  sensation  M  as  exactly  half- 


276  PHYSIOLOGICAL  PSYCHOLOGY. 

way  between  A  and  0.  We  then  seek  to  put  K  half-way 
between  A  and  M\  and  so  on,  until  a  scale  of  graded  least 
observable  differences  is  reached.  But  if  we  follow  the 
other  way  of  applying  this  method  (sometimes  called  "  the 
method  of  minimum  changes  "),  we  seek  directly  to  judge, 
all  along  the  scale  of  intensities,  what  change  of  stimulus 
is  just  enough  to  produce  a  change  in  the  amount  of  the 
resulting  sensation. 

(2)  "The  method  of  average  error"  consists  in  trying 
to  fix  upon  an  amount  of  stimulus  which  will  produce  a 
sensation  that  seems  exactly  equal  to  another   sensation 
selected  as  a  standard  of  estimate.     Repeated  trials  of  this 
sort   result,  of   course,  in  a  number  of   guesses,  some  of 
which  are  more  or  less  out  of  the  way.     By  averaging  all 
the  trials,  the  degree  of  sensitiveness  for  that  sense,  at 
that  place  in  the  scale,  is  determined. 

(3)  In  "the  method  of  correct  and  mistaken  cases," 
trial  is  made  to  see  how  many  right,  and  how  many  wrong, 
guesses  occur  in  the  effort  to  detect  minute  additions  or 
subtractions  in  the  amount  of  stimulus.     Thus :  let  n  = 
the  whole  number  of  guesses,  and  r  =  the  number  of  right 

jl       guesses ;  then  XK=  the  sensitiveness  to  minute  differences, 
/A 

for  that  particular  position  in  the  scale,  and  particular 
kind  of  stimulation.  In  this  way  a  scale  can  be  manufac- 

^t     tured,  —  the  positive  value  of  ^being  kept  unchanged. 

All  three  of  these  methods  are  alike  in  that  they  aim  at 
constructing  a  scale  of  degrees  of  sensitiveness  by  deter- 
mining the  least  observable  differences,  for  all  the  senses, 
and  for  the  various  gross  amounts  of  stimulus,  under  a 
variety  of  circumstances. 

The  Law  of  Weber  or  Fechner.  —  The  attempt  to  formu- 
late the  results  reached  by  thousands  of  experiments,  by 
each  of  the  foregoing  methods,  has  resulted  in  a  "law" 


QUANTITY  OF   SENSATIONS.  277 

known  by  the  name  of  Weber,  or  Fechner.  The  former 
of  these  investigators  propounded  the  principle  of  this 
"  law  "  ;  the  latter  has  defended  and  elaborated  it  by  a 
vast  amount  of  research.  Weber's  law  admits  of  state- 
ment in  several  forms  :  (1)  The  difference  between  any 
two  stimuli  is  experienced  as  of  equal  magnitude  in  case 
the  mathematical  relation  of  those  stimuli  remains  un- 
altered. (2)  If  the  intensity  of  the  sensations  is  to  increase 
by  equal  absolute  magnitudes,  then  the  relative  increase  of 
the  stimulus  must  remain  constant.  (3)  The  strength  of 
the  stimulus  must  increase  in  a  geometrical  proportion  in 
case  the  strength  of  the  sensation  is  to  increase  in  an 
arithmetical  proportion.1 

Value  of  Weber's  Law.  —  Familiar  experience  makes  us 
aware  that  the  difference  in  the  amount  of  our  sensations 
does  not  increase  in  direct  arithmetical  ratio  with  the 
increase  in  the  intensity  of  the  stimuli  which  cause  the  sen- 
sations. For  example,  the  difference  between  the  shadow 
cast  by  one  taper  and  that  cast  by  two  is  readily  observable 
in  a  dimly  lighted  room,  but  is  wholly  unobservable  in 
open  sunlight  ;  or  the  strength  in  the  ticks  of  two  dif- 
ferent clocks  can  be  nicely  discriminated,  but  not  the 

1A  simple  statement  of  Weber's  principle  maybe  given  as  follows: 
Let  //  =  the  intensity  of  the  light  of  one-half  of  a  white  field  ;  -=-  =  the 
smallest  fraction  of  stimulus  added  to  H  that  will  produce  an  observable 

increase  in  this  intensity  ;  and  H+  —  =  the  intensity  of  the  other  half 

100 

of  the  same  field.     Then  let   #=#16  sensation  produced  by  H,  and 

TT 

S  +  s  =  the  sensation  produced  by  JZ  -|  --  :  s  will  now,  of  course,  repre- 

J.UU 

sent  the  so-called  "least  observable  difference"  at  this  point  in  the  scale. 
We  have,  then,  H  produces  S;  fl>  ~p  or  {%%  H,  produces  #+s; 


or  1{$  •  i£$  H,  produces  S+  s  +  s;  and  so  on.    That  is  to 

say,  if  s  is  to  be  kept  of  the  same  magnitude,  then  H  must  be  multiplied 
by  the  same  magnitude  1$$. 


278  PHYSIOLOGICAL   PSYCHOLOGY. 

amount  of  noise  made  by  two  successive  discharges  of  a 
cannon. 

To  the  principle  involved  in  this  familiar  experience 
Weber's  law  attempts  to  give  an  exact  scientific  expression. 
It  has  been  well  said1  that  its  value  depends  upon  its 
furnishing  a  means  of  comparing  the  sensibility  of  differ- 
ent incommensurate  senses.  As  formulated  in  terms  of 
the  method  of  correct  and  mistaken  cases,  it  means  that 
the  standard  by  which  the  relative  qualities  of  our  sen- 
sations are  judged,  is  independent  of  the  absolute  magni- 
tude of  the  stimuli,  but  depends  solely  on  the  ratio  of  the 
stimuli.  As  formulated  by  the  method  of  average  error, 
it  means  that  the  probable  error  will  not  be  influenced 
by  a  change  in  the  absolute  magnitude  of  the  stimulus 
according  to  which  the  adjustments  are  to  be  made. 

After  years  of  diligent  experimenting,  in  countless 
numbers  of  cases,  the  so-called  law  of  Weber  is  weaker 
rather  than  stronger,  in  its  claim  to  be  an  exact  expression 
of  the  universal  relation  between  changes  in  the  intensity 
of  the  stimulus  and  changes  in  the  amount  of  the  resulting 
sensations.  The  most  that  can  be  said  is  this:  The  law 
summarizes  many  facts  reasonably  well  within  a  certain 
range  of  sensations  lying  near  the  middle  of  the  scale  of 
quantity,  and  for  certain  of  the  senses. 

Least  Observable  Difference  in  Sensations  of  Pressure. — 
Various  causes  affect  our  sensations  of  pressure,  as  respects 
their  smallest  discernible  quantity.  Among  them  are  the 
presence  of  muscular  sensations,  mingled  with  sensations 
of  the  skin  (temperature,  etc.),  the  locality  to  which  the 
stimulus  is  applied,  the  interval  of  time  allowed  after 
applying  the  stimulus,  etc.  Weber  ascertained  that,  when 
the  interval  was  15  to  20  seconds,  under  the  most  favor- 
able circumstances,  14^-  could  be  distinguished  from  15 

1  By  Professor  Jastrow,  in  the  American  Journal  of  Psychology,  1888, 
p.  298. 


QUANTITY   OF   SENSATIONS.  279 

grammes  of  pressure,  14J  from  15  ounces,  etc.  That  is, 
some  persons  distinguish  weights  which  differ  in  the  ratio 
of  29 :  30,  when  laid  on  the  volar  side  of  the  last  phalanx 
of  the  finger.  If  allowed  to  raise  and  lower  the  weights, 
the  niceness  of  the  discrimination  is  increased  so  that  the 
ratio  becomes  39  :  40. 

More  recent  experiments  seem  to  show  that  the  quotient 
of  sensitiveness  for  sensations  of  pressure  varies  greatly 
with  the  different  absolute  values  of  the  weights  employed. 
One  calculation  places  it  at  j^  for  weights  of  300  grammes 
to  ^  for  weights  of  3000  grammes.  Another  series  of 
experiments  gave  results  (somewhat  doubtful,  however), 
varying  as  the  following  table  indicates :  — 

Absolute  weight.        Least  observable  difference.         Quotient  of  Sensitiveness. 
Grammes.  Grammes. 

10  0.7  TV 

50  1.7  A 

100  2.4  & 

200  3.6  & 

300  4.6  & 

400  5.2  7V 

450  6.5  & 

500  25.5  & 

When  the  weights  are  raised,  it  would  appear  (according 
to  the  latest  experiments)  that  we  are  influenced  in  our 
estimate  of  their  magnitude  by  the  speed  with  which  they 
rise.  Indeed,  it  is  held  by  some  observers  that  the  entire 
validity  of  Weber's  law  in  such  cases  depends  upon  the 
fact  that  a  just  observable  difference  in  the  speed  of  their 
rise  corresponds  to  a  just  observable  difference  in  their 
weight. 

Lower  Limits  of  Sensations  of  Pressure.  —  The  absolute 
sensitiveness  of  the  different  areas  of  the  skin  to  sensations 
of  pressure  differs  exceedingly.  This  difference  is  due  to 
a  variety  of  circumstances,  —  such  as,  the  number  and  sen- 
sitiveness of  the  nervous  elements  present  in  the  skin,  the 


280  PHYSIOLOGICAL  PSYCHOLOGY. 

thickness  of  the  skin,  its  tension  over  the  underlying 
parts,  attention,  use,  habit,  etc.  Following  are  the  num- 
bers which  have  been  found  to  measure  the  lightest  weight 
which  would  produce  a  sensation  on  various  parts  of  the 
body:  on  the  forehead,  temples,  and  dorsal  side  of  the 
fore-arm  and  hands,  0.002  gramme ;  volar  side  of  the  fore- 
arm, 0.003  gramme ;  nose,  lips,  chin,  eyelids,  and  skin  of 
abdomen,  0.005  gramme ;  volar  side  of  the  fingers,  0.005- 
0.015 ;  finger-nails  and  skin  of  the  heel,  1  gramme. 

Quantity  of  Temperature-sensations.  —  It  is  nearty  impos- 
sible to  apply  Weber's  law  to  sensations  of  heat  and  cold. 
We  do  not  know  exactly  what  to  measure  as  constituting 
the  quantitative  changes  in  temperature.  The  temperature 
of  the  so-called  "  zero-point  of  the  skin  "  is  very  change- 
able. The  one  rule  which  seems  most  general  is  this: 
The  skin  is  most  sensitive  to  changes  which  lie  near  its  own 
zero-point.  The  nicest  discrimination  of  two  temperatures 
is  attained  where  one  lies  just  a  little  above,  and  the  other 
just  a  little  below,  this  zero-point.  Under  such  circum- 
stances, changes  will  be  read  by  the  skin  amounting  to 
only  V  or  ^  F. 

We  have  already  seen  (p.  239  f .)  that  the  sense  of  tem- 
perature depends  for  its  fineness  upon  the  extent  and 
locality  of  the  surface  of  the  skin  which  is  excited.  Since 
the  modern  discovery  of  heat-spots  and  cold-spots  that  can 
be  located,  with  different  degrees  of  intensity  and  in  vary- 
ing numbers,  011  the  different  areas  of  the  body,  the  table 
of  sensitiveness  to  temperature  has  been  greatly  changed. 
In  general,  it  may  be  said  that  the  sensitiveness  of  the 
forehead  to  cold  is  intense,  but  to  heat  only  moderate  ;  that 
of  the  breast  to  cold  moderate  along  the  sternum,  and 
elsewhere  very  intense,  while  to  heat  it  is  only  moderate, 
except  near  the  nipples ;  that  of  the  back  everywhere  very 
intense  to  cold,  and  only  moderate  to  heat;  while  in  all 


QUANTITY   OF   SENSATIONS.  281 

parts  of  the  hand  the  intensity  of  sensitiveness  is  nearly 
alike  for  both  cold  and  heat. 

Measure  of  the  Stimulus  for  Sensations  of  Sound.  —  If 
the  quantity  of  our  sensations  of  sound  varied  in  direct 
proportion  to  the  intensity  of  the  stimulus,  it  would  be 
impossible  to  execute  nicely  shaded  passages  of  music. 
How  exactly  the  law  of  Weber  applies  to  musical  sounds, 
it  is  difficult  to  tell  because  the  experiments  are  necessarily 
complicated  with  so  many  conditions.  We  have  already 
seen  that  no  considerable  increase  in/  the  intensity  of  a 
tone  is  possible  without  changing  its  timbre.  Pitch  also 
has  a  great  influence  upon  our  estimates  of  intensity.  In 
experimenting  with  noises  the  absence  or  presence  of  so- 
called  "entotic"  sounds  (sounds  that  originate  in  the 
action  of  physiological  changes  within  the  organs  contigu- 
ous to  the  inner  ear)  is  of  great  influence.  The  order  in 
which  the  sounds  are  heard  seems  also  to  have  something 
to  do  with  our  impressions  of  their  loudness.  Of  two 
successive  equal  sounds  the  second  regularly  seems  the 
greater. 

It  is  also  a  matter  of  some  dispute  whether  the  intensity 
of  the  acoustic  stimulus  is  to  be  measured  by  the  product 
of  the  mass  of  the  falling  body  into  the  height  from  which 
it  falls  (m  X  li) ;  or  by  the  product  of  the  mass  into  the 
square  root  of  the  height  (m  x  -\/li).  The  former  mode 
of  measurement  is  probably  more  correct. 

Weber's  Law  applied  to  Sensations  of  Sound.  —  By  making 
large  allowances  for  relations  of  time,  and  using  the  method 
of  correct  and  mistaken  cases,  some  of  the  older  experi- 
menters succeeded  in  establishing  the  law  of  Weber  as 
fairly  accurate  for  sensations  of  noise  of  moderate  intensity. 
More  recent  researches  still  leave  the  matter  in  doubt, 
however;  at  any  rate,  unexplained  variations  of  the  so- 
called  law  arise  at  various  points  along  the  scale,  and  near 
the  upper  and  lower  limits  it  seems  to  fail  completely. 


282  PHYSIOLOGICAL  PSYCHOLOGY. 

The  sensitiveness  of  the  ear  for  minute  differences  in 
the  intensity  of  sensations  of  tone  seems  to  be  greater  than 
that  for  noise.  But  here  the  variations  from  Weber's  law 
are  numerous.  The  following  tables  sum  up  the  results 
of  two  recent,  extended  sets  of  experiments.  In  the  first 
the  unit  of  measure  for  the  strength  of  the  tone  was  taken 
"  below  the  threshold,"  and  the  fraction  of  "  discriminative 
sensibility  "  is  given  for  the  different  places  on  the  scale 
marked  by  different  multiples  of  this  unit  of  intensity. 
[The  threshold  value  was  about  1.6,  as  expressed  in  units 
of  the  same  intensity.] 

Intensity.  Discriminative  sensibility. 


Intensity.  Discriminative  sensibility. 

5  .135 

20  .108 

102  .112 

10«  .118 

10*  .116 

105  .131 


106  .140 

107  .153 

108  .161 

109  .178 

1010  .225 

1011  .350 


Of  course,  if  Weber's  law  held  exactly  the  fraction  in 
the  second  column  of  the  table  would  remain  unchanged. 

By  using  tuning-forks  and  the  method  of  "  just  observ- 
able difference,"  another  observer  obtained  the  following 
results :  — 

Number  of  vibrations 64    128    256    512   1024  2048 

Just  observable  difference 149   .159    .232   .251     .218    .362 

Fraction  demanded  by  Weber's  law      .15     .30     .60   1.20    2.40    4.80 

In  this  table  we  note  a  wide  discrepancy  between  the 
fraction  of  just  observable  difference  as  determined  by 
actual  experiment  and  that  demanded  by  the  law  of 
Weber. 

Lower  Limit  of  Sensations  of  Sound.  —  The  least  amount 
of  sound  which  will  excite  sensation  depends,  of  course, 
upon  many  circumstances.  Of  these  the  most  important  is 
as  nearly  perfect  stillness  as  it  is  possible  to  obtain.  Under 
the  most  favorable  conditions  an  incredibly  small  amount 


QUANTITY   OF   SENSATIONS.  283 

of  energy  expended  011  the  ear  will  excite  sensation.  One 
observer  has  fixed  the  limit  at  the  noise  made  by  a  cork 
ball  of  1  milligramme  (about  0.0154  grain)  weight  falling 
from  a  height  of  1  millimeter  (0.03937  inch).  Another 
has  calculated  that  an  amplitude  in  the  molecules  of  the 
air  not  more  than  -^  the  wave-length  of  green  light,  doing 
upon  the  ear-drum  only  about  yV  of  the  work  done  upon 
the  same  surface  of  the  pupils  of  the  eye  by  a  single 
candle,  will  evoke  a  sensation  of  sound.  Yet  another 
calculation  fixes  the  energy  at  the  threshold,  for  a  musical 
tone  of  440  vibrations,  as  about  ^  that  for  sight  (e.g.  of 
the  light  of  a  star  of  the  sixth  or  seventh  magnitude). 

Astronomers  were  for  a  long  time,  before  the  promul- 
gation of  Weber's  law,  aware  of  the  fact  that  the  magni- 
tudes of  the  stars  are  not  to  be  classified  according  to  their 
absolute  brightness  as  determined  by  photometric  observa- 
tions. Sir  John  Herschel  assumed  this  when  he  made  the 
series  of  magnitudes  run  1:2:3:4,  etc.,  while  the  series 
according  to  photometric  brightness  run  1 :  \  :  ^  :  y1^ ,  etc. 
Something  like  the  same  principle  is  required  to  account 
for  our  ordinary  experience  with  sensations  of  light.  The 
finer  gradations  of  shade  in  a  lithograph  or  photograph 
are  not  lost  when  we  take  it  from  the  open  sunlight  into 
a  dimly  lighted  room.  Some  principle  resembling  Weber's 
law  is  necessary  to  account  for  this. 

Measure  of  the  Stimulus  for  Sensations  of  Sight.  —  The 
accurate  measurement  of  visual  sensations  is  complicated 
with  the  facts  that  the  retina  has  a  "  light  of  its  own," 
and  that  the  laws  of  change  in  quality  operate  to  obscure 
the  laws  of  the  change  in  quantity.  Earlier  experiments 
took  the  form  of  determining  the  distance  to  which  a 
candle  must  be  removed  from  an  object  in  order  that  the 
shadow  produced  by  its  light  might  disappear  in  the  shadow 
produced  by  another  candle  of  like  power  but  situated  at 


284  PHYSIOLOGICAL  PSYCHOLOGY. 

a  fixed  near  distance  from  the  object.  It  was  thus  dis- 
covered that  marked  variations  occur  when  we  diminish 
considerably  the  light  of  the  background  on  which  the 
shadows  are  cast ;  and  that  the  quotient  which  represents 
the  least  observable  difference  varies  with  the  different 
intensities  of  the  light  employed. 

Helmholtz  and  other  late  observers  have  used  rotating 
disks  with  small  black  stripes  upon  their  white  surfaces 
(  " Masson's  Disks").  The  grayish  circles  made  by  the 
admixture  of  the  color  of  the  stripes  with  that  of  the  sur- 
faces are  then  compared,  as  a  test  of  the  eye's  sensitiveness 
to  minute  differences.  The  experiment  may  be  varied  by 
looking  at  these  disks  through  gray  glasses  of  varying 
intensity.  In  experimenting  with  color-tones  the  method 
may  be  used  of  comparing  a  white  surface  with  one  in 
which  colored  light  has.  been  mixed  with  the  white. 

The  later  experiments  seem  to  show  that  the  effect  of 
background  is  enormous ;  and  that  the  absolute  strength 
of  the  stimulus  used  is  also  very  important. 

Weber's  Law  applied  to  Sensations  of  Sight,  —  The  earlier 
experiments,  conducted  under  the  supervision  of  Fechner, 
were  held  to  show  that  the  law  of  Weber  applies  to  sensa- 
tions of  light ;  and  that  the  least  observable  difference,  for 
absolute  values  of  moderate  intensity,  is  about  y^-, —  this 
being  the  smallest  average  difference  in  the  brightness  of 
the  shadows  which  the  eye  can  detect.  But  subsequent 
observations  found  the  quotient  to  vary  from  ^  f°r  weak 
intensities  of  light  to  y^  for  stronger  intensities.  Helm- 
holtz placed  the  medium  value  of  the  quotient  of  least 
observable  difference  at  y^:  Aubert  found  a  variation 
of  from  yfj-  to  yl-Q-,  even  when  not  using  absolute  values 
of  light  above  the  middle  of  the  scale  of  intensity.  If  care 
is  taken  to  exclude  disturbances  from  changes  in  the  ad- 
justment of  the  eye,  from  retinal  exhaustion,  reflection  of 
the  light  from  surrounding  objects,  etc.,  it  seems  probable 


QUANTITY   OF   SENSATIONS.  285 

that  Weber's  law  expresses  the  facts  approximately  well  for 
sensations  of  light,  when  the  strength  of  the  stimulus  is  kept 
within  the  middle  ranges  of  the  scale  of  intensities. 

The  same  conclusion  is  apparently  warranted  with 
respect  to  sensations  of  color.  The  quotient  of  least 
observable  difference  is  found  to  be  different,  however,  for 
the  different  color-tones.  Perfect  agreement  is  not  yet 
secured  as  to  the  nature  of  this  difference :  thus  while  one 
observer  has  adopted  the  quotients,  yV  for  red,  -fa  for 
yellow,  -^g-  for  green,  y^-  for  blue,  -^  for  violet,  others 
make  the  sensitiveness  of  the  eye  greatest  for  changes  in 
green  rather  than  violet. 

Lower  Limit  of  Sensations  of  Light.  —  The  least  intensity 
of  light  which  will  produce  any  sensation  at  all  was  given 
by  Aubert  at  -g-J-g-  of  that  reflected  from  white  paper  in  the 
light  of  the  full  moon.  Individual  differences  are  here, 
however,  so  potent  that  all  such  calculations  are  very 
uncertain.  There  is,  indeed,  some  evidence  to  show  that 
certain  persons  are  so  extremely  sensitive  as  to  detect  the 
presence  of  stimulus  that  lies  far  below  the  "threshold" 
of  the  average  consciousness. 

Quantity  of  Sensations  of  Taste.  —  It  seems  quite  impossi- 
ble to  test  by  experiment  the  applicability  of  Weber's  law 
to  sensations  of  taste.  The  conditions  under  which  the 
stimulus  is  applied,  and  its  effect  noted,  are  such  as  not  to 
admit  of  giving  scientific  exactness  to  such  experiment. 
The  importance  of  individual  idiosyncrasies  in  sensations  of 
this  sense  is  too  well  known  to  need  mention. 

Many  experiments  designed  to  fix  the  "  lower  limit "  of 
the  sensations  of  taste  have  yielded  very  interesting  results. 
They  show  the  astonishing  tenuity  of  some  forms  of  stim- 
ulus which  will  secure  an  appreciable  effect  in  conscious- 
ness. The  following  facts  are  interesting  as  bearing  on 
this  point,  rather  than  instructive  as  suggesting  any  law 
of  the  nervous  system  or  of  the  mind. 


286  PHYSIOLOGICAL  PSYCHOLOGY. 

Experiments  in  testing  the  effect  of  seven  vegetable 
bitters  on  forty  persons  yielded  these  results :  of  salicine, 
1  part  in  12,000  parts  of  water  was  detectable  ;  of  mor- 
phine, 1  in  14,000 ;  of  quinine,  1  in  76,000  (some  observers 
have  claimed  to  detect  1  part  in  1,000,000) ;  of  quassine, 
1  in  9000;  picro-toxine,  1  in  197,000  ;  of  aloine,  1  in  210,- 
000 ;  of  strychnine,  1  in  826,000  (twelve  tasters  detected 
1  part  in  1,280,000). 

The  following  table  involves  a  comparison,  with  respect 
to  sensitiveness  of  taste,  between  the  males  and  the  females 
experimented  upon :  — 

Object  tested.  Male  observers.  Female  observers. 

Quinine 1  part  in  392,000 456,000 

Sugar  (cane) 199 204 

Acid  (sulph.)      .,.,...     2,080 3,280 

Soda  (bicarb.) 98  .....  126 

Salt 2,240 1,980 

In  general,  a  smaller  absolute  quantity  of  stimulus, 
when  in  a  relatively  concentrated  solution,  will  suffice  to 
excite  the  end-organs  of  taste. 

Quantity  of  Sensation  of  Smell. —  The  sense  of  smell  has  a 
great  degree  of  "  sharpness,"  or  capacity  for  excitement  by 
small  quantities  of  stimulus,  as  distinguished  from  "  fine- 
ness," or  power  to  distinguish  minute  variations  in  the 
sensations.  No  experimental  testing  of  the  applicability 
of  Weber's  law  to  sensations  of  this  sense  seems  practi- 
cable. 

Incredibly  small  quantities  of  some  substances  will 
excite  sensations  of  smell.  One  experimenter  found  that 
a  current  of  air  containing  -^-Qinmr  °f  vapor  of  bromine 
excited  a  strong  unpleasant  sensation.  Atmosphere  pol- 
luted with  rro^T»7nr  of  sulphuretted  hydrogen  could  be 
detected.  It  was  calculated  that  Tinmnnr  milligramme  of 
musk  was  the  least  perceivable  amount.  A  recent  report 
is  based  upon  experiments  conducted  by  dissolving  the 


QUANTITY  OF  SENSATIONS.  287 

smellable  substances  in  alcohol,  sprinkling  them  in  an 
empty  closed  room  with  an  atomizer,  and  mixing  them 
with  the  air  with  a  fan.  It  was  thus  found  that  a  sub- 
stance called  "mercaptan"  could  be  detected  in  volu- 
metric proportion  to  the  air  of  only  1  to  50,000,000,000. 
It  was  thus  calculated  that  ^rsrrirffTnrtf  milligramme  of  this 
substance  must  excite  sensation.  The  minuteness  of 
this  quantity  may  be  faintly  imagined  when  we  remember 
that  TW<nnnF  milligramme  of  soda  is  about  as  little  as  can 
be  detected  by  the  microscope. 

On  referring  to  what  was  said  (p.  277  f.)  of  the  value  and 
significance  of  Weber's  law  we  find  our  statements  con- 
firmed. Among  the  more  cautious  observers  the  conclu- 
sion has  been  forming  itself  as  the  result  of  years  of 
experiment,  involving  thousands  of  cases,  that  the  facts  to 
which  the  law  appeals  can  be  summarized  equally  well  in 
several  formulae ;  and  that  none  of  these  formulae  hold 
good  without  many  important  exceptions.  These  excep- 
tions have  to  do,  in  part  at  least,  with  laws  of  perception 
and  judgment  to  which  reference  will  subsequently  be 
made. 

Interpretation  of  Weber's  Law0  —  Previous  to  experiment 
and  scientific  observation  we  should  be  inclined  to  suppose 
that  the  strength  of  the  resulting  sensation  would  vary  in 
direct  proportion  to  the  strength  of  the  stimulus.  But  we 
have  seen  that  this  is  not  so.  The  law  proposed  by  Weber, 
and  elaborated  and  defended  by  Fechner,  holds  that  the 
sensations  vary  in  quantity  in  an  arithmetical  proportion 
while  the  stimuli  vary  in  a  geometrical  proportion.  The 
so-called  "  law  "  turns  out  to  be  only  one  formula,  which 
we  may  adopt  in  connection  with  others,  to  express  the 
facts  approximately  for  certain  classes  of  the  sensations 
when  they  have  a  moderate  intensity,  and  when  our  esti- 
mate of  them  is  undisturbed  by  conditions  extraneous  to 
their  simple  characteristic  of  quantity.  How  shall  this 


288  PHYSIOLOGICAL   PSYCHOLOGY. 

law  —  or  these  formulae  —  be  interpreted?  Three  forms  of 
explanation  have  been  proposed  in  answer  to  this  inquiry. 

The  psycho-physical  explanation  of  Weber's  law  was 
adopted  by  its  distinguished  advocate,  the  physicist  Fech- 
ner.  This  explanation  insists  upon  making  the  law  one 
of  the  widest  application  and  highest  import,  as  stating 
the  relations  between  organic  and  spiritual  activities. 
Fechner  made  the  law,  indeed,  a  basis  for  far-reaching 
philosophical  speculation  regarding  the  world  of  matter 
and  mind.  It  need  scarcely  be  said  that  we  find  absolutely 
no  warrant  for  such  a  view. 

The  physiological  explanation  holds  that  the  law  of 
Weber  applies  to  the  relation  between  the  stimulus,  re- 
garded as  a  mode  of  energy  external  to  the  body,  and  the 
amount  of  physiological  action  which  it  occasions  in  the 
nervous  elements  which  it  excites.  The  law  may  then  be 
considered  as  one  instance  of  a  larger  "  neuro-physic " 
law  which  applies  to  all  stimuli  that  diminish  the  excita- 
bility of  the  organism  on  which  they  act.  Of  this  larger 
law  the  formula  might  run  somewhat  as  follows :  "  The 
excitation  caused  by  a  change  of  intensity  in  a  stimulus 
that  diminishes  excitability  remains  the  same,  if  the  re- 
lation of  the  change  of  intensity  to  the  intensity  on  the 
basis  of  which  the  change  is  made  remains  the  same." 
This  rule  holds  good,  however,  only  under  similar  condi- 
tions and  within  certain  limits  of  absolute  intensity  of 
the  stimulus.  "  Outside  these  limits  ...  an  increase  of 
excitation  occurs  with  small,  and  a  decrease  with  great-, 
intensity." 

The  psychological  explanation  of  Weber's  law  resolves  it 
into  a  special  case  under  the  greater  law  of  the  relativity 
of  our  inner  states.  In  general,  it  may  be  said  that  every 
mental  state  has  its  value,  determined,  both  as  respects  its 
quality  and  its  so-called  quantity,  ly  its  relation  to  other 
mental  states.  It  is  the  amount  of  change  which  mental 


QUANTITY   OF   SENSATIONS.  289 

apperception  chiefly  appreciates.  Hence  the  important 
influence  that  attention,  interest,  habit,  contrast,  natural 
power  of  discrimination,  etc.,  have  upon  those  "  estimates  " 
on  which  we  have  to  rely  for  a  formula  like  that  called 
Weber's  law. 

It  seems  to  us  undoubted  that  both  the  physiological 
and  the  psj^chological  interpretation  are  necessary  in  order 
to  understand  the  significance  of  whatever  truth  belongs 
to  this  celebrated  so-called  "  law  "  of  the  relation  between 
changes  in  the  intensity  of  the  stimulus  and  the  resulting 
changes  in  the  quantity  of  our  estimated  sensations. 


CHAPTER  XIII. 

PERCEPTION  BY  THE  SENSES. 

THERE  is  a  very  wide  difference  between  having  sen- 
sations, however  intense  and  complex,  and  knowing  the 
qualities  of  things  by  use  of  the  senses.  Sensations,  in 
themselves  considered,  are  plainly  psychical  states ;  and, 
as  such,  they  are  devoid  of  a  locality,  or  even  an  existence, 
external  to  the  mind.  But  things  are  known  as  so-called 
objective  or  eotfra-mental  existences;  they  are  all,  as  we 
are  wont  to  say,  extended  and  related  to  one  another  "  in 
space."  Indeed,  the  one  characteristic  which  things  pos- 
sess, as  perceived  by  us,  but  which  does  not  belong  to  the 
simple  sensations  which  are  the  factors  of  the  perceptions, 
is  their  space-form. 

Now  a  study  of  the  development  of  the  mind  shows 
indisputably  that  the  perception  of  things  does  not  come 
at  once.  We  all  have  to  learn  to  know  things,  —  their 
space-qualities  and  spatial  relations.  As  we  shall  see  sub- 
sequently, it  is  not  altogether  out  of  the  way  to  say  that 
we  have  to  learn  to  construct  things  perceived,  in  order  to 
perceive  them.  The  general  problem  which  physiological 
psychology  has  to  solve  in  this  field  of  inquiry  may,  then, 
be  stated  as  follows :  On  the  basis  of  what  combinations 
of  physical  processes  of  sense  do  the  different  resulting  sen- 
sations come  to  be  combined  into  perceptions  of  things,  under 
the  new  characteristic  of  space-form  ? 

In  treating  this  branch  of  the  subject,  the  method  which 
we  have,  in  the  main,  followed  thus  far,  may  profitably  be 
reversed.  It  will  make  the  whole  of  this  difficult  matter 
290 


PERCEPTION   BY  THE   SENSES.  291 

clearer  if  we  give,  first,  a  sketch  of  the  general  psycho- 
logical theory  of  perception,  and  then  speak,  afterward,  of 
particular  forms  of  perception  as  illustrating  the  general 
theory. 

GENERAL  THEORY  OF  PERCEPTION  BY  THE  SENSES. 

The  fact  that  perception  by  the  senses  implies  such  a  very 
complex  and  long-continued  evolution  of  the  mind  makes 
its  scientific  analysis  both  more  difficult  and  more  neces- 
sary. The  ordinary  operations  of  consciousness  are  wholly 
unable  to  do  anything  adequate  toward  making  the  requi- 
site analysis. 

"Common-sense"  View  of  Perception  Erroneous.  —  We 
cannot  look  on  any  complex  object  —  for  example,  a  land- 
scape—  without  the  conviction  that  we  are  immediately 
being  impressed  with  a  faithful  copy  of  what  exists  wholly 
external  to  us,  in  reality.  These  eatfra-mental  beings  and 
the  events  which  happen  between  them  are,  in  the  judg- 
ment of  so-called  "  common-sense,"  quite  enough  to  account 
for  our  perceptions.  Indeed,  they  form  the  only  necessary 
or  possible  explanation  of  these  perceptions. 

Scientific  psychology  shows  that,  strictly  speaking,  beings 
and  happenings  outside  of  our  minds  and  bodies,  in  them- 
selves, furnish  no  explanation  whatever  for  our  percep- 
tions. They  are  and  can  be  nothing  to  us,  except  as  they 
affect  us.  They  affect  us  only  by  action  on  the  nervous 
system,  —  beginning  with  the  end-organs  of  sense,  continu- 
ing along  the  sensory  nerve-tracts,  and  issuing  in  cerebral 
changes.  But  such  induced  activities  of  the  nervous  sys- 
tem are  nothing  to  us,  as  minds,  unless  they  are  followed 
or  accompanied  by  psychical  changes.  It  is,  indeed,  only 
as  necessary  physical  conditions  of  the  psychical  changes 
that  they  can  be  said  to  be  either  the  explanation  or  the 
object  of  our  perceptions. 

Physiological  View  of  Perception  Inadequate.  —  But  if  the 


292  PHYSIOLOGICAL   PSYCHOLOGY. 

unscientific  view  of  the  nature  of  perception  by  the  senses 
is  illusory,  the  view  of  physiological  science  alone  is  inad- 
equate. Indeed,  the  latter  may  be  so  represented  as  only 
to  continue,  in  a  more  elaborate  but  indefensible  form,  the 
illusions  of  the  ordinary  impression.  This,  for  example, 
is  the  case  whenever  the  physical  image  formed  on  the 
retina  is  considered,  in  itself,  to  account  for  the  mental 
perception  of  the  visual  object.  The  nervous  processes 
which  result  from  that  orderly  arrangement  in  the  action 
of  the  stimulus  upon  the  end-organs,  which  appears  as  a 
retinal  image  to  the  inspection  of  another  observer,  is  in- 
deed a  necessary  physical  condition  of  our  clear  perception 
of  the  object.  But  the  retinal  image  never  becomes  a  kind 
of  inner  object  for  our  own  brain  or  mind.  The  same 
thing  is  true  of  the  orderly  arrangement  of  the  excited 
elements  in  the  cerebral  substance  itself.  There  is  no 
brain-image,  copied  from  the  object,  which  the  mind  can 
immediately  contemplate ;  and.  if  there  were,  we  should 
need  another  eye  connected  with  another  brain  to  make 
use  of  it. 

Neither  does  the  accurate  physiological  description  of 
the  construction  of  the  peripheral  areas  upon  which  the 
stimulus  acts  furnish,  in  itself,  any  reason  for  the  percep- 
tion of  these  areas  as  in  space,  or  for  distinguishing  them 
from  other  areas  nearer  or  more  remote.  To  regard  the 
mind  as  diffused  through  or  over  the  surface  of  the  skin, 
taking  note  —  as  it  were  —  of  the  condition  of  this  organ, 
or  of  the  presence  of  the  bodies  with  which  it  is  in  contact, 
is  exceedingly  crude  and  erroneous. 

The  Factors  and  Processes  of  Perception  Psychological.  —  A 
true  theory  of  the  nature  and  growth  of  that  knowledge  of 
things  which  comes  through  the  senses  must  always  be  dis- 
tinctively psychological.  For  all  the  factors  built,  as  it 
were,  into  the  products  which  we  call  "  perceptions  "  are 
mental ;  as  we  have  already  seen,  these  factors  are  sensa- 


PERCEPTION  BY  THE  SENSES.          293 

tions  and  sensation-complexes.  The  process  of  building, 
whether  it  be  accomplished,  for  any  object,  more  slowly  or 
with  what  appears  as  a  practical  instantaneousness,  is  a 
mental  process.  The  development  of  the  capacity  for  this 
process  is  the  result  of  a  mental  evolution.  These  truths 
must  be  admitted,  from  whatever  point  of  view  our  study 
of  perception  is  conducted.  It  is  as  necessary  for  physio- 
logical psychology  to  admit  these  truths  as  for  psychology 
studied  from  the  introspective  point  of  view. 

With  these  preliminary  remarks,  we  enumerate  the  fol- 
lowing considerations  as  necessary  to  any  true  theory  of 
perception  by  the  senses. 

(1)  Synthesis  of  Sensations  Necessary,  —  In  order  to  ex- 
plain those  steps  by  which  the  mere  having  of  sensations 
issues  in  the  perception  of  objects  by  the  senses,  we  must 
assume  that  a  combination  of  two  or  more  qualitatively 
different  series   of   sensation-complexes  has   taken  place. 
This  combination  is  sometimes  spoken  of  as  an  "associa- 
tion"   of    sensations.      But    the   word   "association,"    on 
account  of  its  established  use  to  denote  relations  formed 
in  time  amongst  different  mental  images,  is  not  well  suited 
to   express   the  combination  of  sensations  and  sensation- 
complexes,   with   one   another   and   with    their    memory- 
images,  to  form  an  object  of  sense.     Such  combination  is 
rather  of  the  nature  of  a  chemical  fusion  (if  we  may  bor- 
row from   physical   processes   and  products    a   figure   of 
speech),  in  which  the  factors  lose  their  individuality,  and 
the  resulting  compound  product  is  determined  by  all  the 
factors,  without  appearing  to  contain  them.      The  word 
"  synthesis  "  is  selected  to  describe  such  a  process  of  psy- 
chical uniting. 

(2)  Spatial  and  Non-spatial  Series  of  Sensations.  —  Series 
of  sensations  which  arise  in  the  mind,  on  successive  irrita- 
tion of  closely  contiguous  portions  of  the  sense-organ,  are 
fitted  to  enter  into  the  process  of  "psychical  synthesis," 


294  PHYSIOLOGICAL  PSYCHOLOGY. 

Series  of  other  sensations  belonging  to  a  different  class  of 
senses  are  not  thus  fitted.  The  former  may  be  called 
"spatial  series  '  of  sensations;  the  latter,  "non-spatial'* 
series  of  sensations.  Senses  whose  excitation  gives  rise  to 
spatial  series  of  sensations  may  be  called  "geometrical 
senses '' ;  those  that  produce  only  non-spatial  series  of  sen- 
sations may  be  called  "  non-geometrical  senses.'* 

For  example  :  sensations  of  smell  are  obviously  not  fitted 
to  form  a  so-called  spatial  series ;  indeed,  they  are  incapa- 
ble of  being  arranged  in  any  series  whatever.  A  being 
possessed  of  mere  sensations  of  smell,  without  any  of  the 
tactile  or  muscular  sensations  which  accompany  those  sen- 
sations in  the  case  of  man,  would  have  —  so  to  speak  —  no 
elements  from  which  to  construct  objects  of  sense.  The 
sense  of  smell  is  decidedly  non-geometrical.  On  the  con- 
trary, we  shall  see  that  sensations  of  the  eye  and  of  the 
skin  are  of  the  "  spatial-series  "  kind.  These  organs  are 
the  leading,  and  we  believe  —  with  the  sensations  of  the 
muscles,  joints,  etc.  —  the  only  geometrical  senses.  By 
use  of  these  senses  we  construct  a  world  of  objects  having 
spatial  qualities  and  set  in  relations  of  space. 

(3)  Need  of  Local  Signs.  —  The  locally  different  parts  of 
the  organs  of  the  geometrical  senses  must  each  have  some 
mental  representative  in  the  sensations  which  stimulation 
of  each  calls  forth.  As  parts  of  the  physical  organism, 
they  have  no  significance  for  the  mind.  Only  the  psychical 
changes  which  their  irritation  causes  can  become  factors  in 
the  psychical  products  and  processes  of  perception.  The 
theory  of  perception  seems  then  to  demand  the  assumption 
that  all  sensation-complexes,  which  are  to  become  factors 
of  perception,  must  have  a  peculiar  "  local  stamp,"  or 
shade,  or  mixture  of  quality,  —  dependent  upon  the  place 
of  the  organ  at  which  the  stimulus  is  applied.  This 
peculiar  local  stamp,  or  shade,  or  mixture  of  quality  is 
called. a  "local  sign."  It  is  to  the.  philosopher  Lotze  that 


PERCEPTION  BY  THE  SENSES.          295 

we  owe  the  first  elaborate  theory  of  "  local  signs  "  and  their 
relation  to  the  formation  of  the  perception  of  objects  by 
the  senses. 

(4)  Stages  of  Perception,  —  To  perceive  objects  of  sense 
is  something  which  must  be  learned  by  every  human  mind. 
This  is  as  true  of  objects  near  as  of  those  remote ;  of  the 
organs  of  our  own  body,  as  seen  or  felt  by  ourselves,  as  of 
the  distant  mountain  or  the  fixed  star.     The  end  aimed  at 
by  nature,  so  to  speak,  is  the  clear  and  accurate  construc- 
tion of  a  "  field  of  vision  "  and  a  "  field  of  touch,"  by  the 
two   great   geometrical   senses.     Perception  is   then  —  we 
can  scarcely  repeat  or  emphasize  the  declaration  too  much 
—  a  mental  achievement. 

In  the  one  work  of  perception  two  particularly  note- 
worthy stages  are  to  be  recorded.  These  are  the  "  locali- 
zation "  and  the  "  objectifying,"  or  "  eccentric  projection," 
of  the  sensation-complexes.  By  the  former  we  understand 
the  transference  of  these  sensation-complexes  from  mere 
psychical  states  to  processes  or  conditions  recognized  as 
belonging  to  more  or  less  definitely  fixed  points  or  areas  of 
the  extended  body.  By  the  latter  we  understand  the  giving 
to  these  sensation-complexes  an  "  objective  "  existence,  as 
qualities  of  objects  (so-called  "  things  "),  situated  within  a 
field  of  space  and  in  contact  with,  or  more  or  less  remotely 
distant  from,  the  body. 

(5)  Characteristics  of  the  Spatial-series.  —  In  the  process  of 
perception  by  the  senses,  some  of  the  many  different  sen- 
sation-complexes come  to  be  localized  as  affections  of  the 
different   parts  of    our  own  bodies ;    some   of   them    also 
become  projected  —  so  to  speak  —  outside  of    our  bodies 
as  qualities  of  things,  either  in  contact  with  our  bodies 
or  situated  at  a  distance  from  them.     But  not  all  kinds 
of  sensation-complexes  —  it  has   been  said  —  lend  them- 
selves to  this  kind  of  constructive  treatment.     Not  all  of 
them  organize   themselves   into   a  world   of   independent 


296  PHYSIOLOGICAL  PSYCHOLOGY.   . 

realities,  spatially  extended  and  spatially  related.  We 
inquire  then,  What  characteristics  must  the  series  of  sen- 
sation-complexes, arising  through  excitement  of  the  organ 
of  sense,  possess  in  order  to  lend  themselves  to  this  synthe- 
sizing and  organizing  process  ? 

Plainly  it  will  not  do  to  suppose  that  any  two  sensation- 
complexes,  in  order  to  combine  in  the  construction  of  an 
object,  must  originate  through  the  excitement  of  elements 
of  the  organ  that  actually  lie  side  by  side.  The  object 
perceived  is  indeed  made  up  of  parts  contiguous  in  space. 
But  the  extension  of  the  object  perceived  is  never  a  copy 
of  the  extension  of  that  nerve-expanse  of  the  eye  or  skin, 
by  irritation  of  whose  minute  parts  the  object  is  presented 
to  the  mind.  For  example,  the  nervous  elements,  on  whose 
irritation  the  perception  of  an  extended  visual  object 
depends,  lie  in  the  retinas  of  two  eyes.  Each  retinal 
image  is  interrupted  by  the  "  blind-spot."  The  images  have 
no  value  for  perception  unless  the  results  of  the  irritation 
are  propagated  to  the  brain.  In  the  brain,  we  know  that 
the  nervous  elements,  whose  irritation  results  in  the  per- 
ception of  the  extended  visual  object,  do  not  lie  at  all  side 
by  side  after  the  exact  manner  of  the  parts  of  the  object 
itself. 

It  is  not  necessary  to  perception  that  the  nervous  ele- 
ments concerned  in  the  production  of  the  extended  object 
shall  themselves  sustain  certain  spatial  relations  to  each 
other.  What  is  necessary  is  that  the  series  of  sensation- 
complexes  which  result  from  the  irritation  of  these  nervous 
elements  shall  be  capable  of  definitely  and  reciprocally 
determining  each  other  as  series  of  sensations.  To  accom- 
plish this,  several  characteristic  qualities  are  necessary. 

A.  Spatial-series  of  sensations  must  include  sensations  of 
similar  quality  that  admit  of  easy,  rapid,  and  frequent  repe- 
tition in  varying  order  of  arrangement.  Senses  which,  like 
the  eye  and  hand,  have  organs  capable  of  rapid,  precise, 


PERCEPTION  BY  THE  SENSES.          297 

and  nicely  graded  motion,  are  obviously  equipped  with 
that  peripheral  mechanism  which  is  favorable  to  the  pro- 
duction of  spatial  series  of  sensations.  In  the  use  of  the 
eye,  for  example,  there  are  produced  various  intermingling 
simple  sensations  of  light  and  color-tones,  together  with 
muscular  sensations  of  accommodation  and  of  motion  due 
to  the  action  of  the  six  muscles,  and  sensations  of  tactual 
sort  as  the  eye  rolls  in  its  socket,  etc.  Moreover,  these 
series  of  sensations  thus  evoked  are  capable  of  repetition  ; 
not  only  forward  in  the  order  of  a,  /3,  7,  S,  .  .  .  /*,  or  in 
the  reverse  order  of  /£,  X,  *,  .  .  .  /3,  a,  but  also  in  an  end- 
less variety  or  an  interlacing  network  of  fused  sensation- 
complexes. 

The  same  thing  holds  true  of  the  series  of  sensations 
of  light  pressure,  fused  with  factors  derived  from  that 
unclassifiable  crowd  of  other  sensations  located  in  the  skin, 
as  the  hand  moves  over  some  object,  or  as  an  object  is 
moved  over  some  surface  of  the  body.  The  same  thing  we 
believe  to  be  also  true  of  the  muscular  sensations,  —  though 
upon  this  point  there  is  more  reason  for  doubt  and  differ- 
ence of  view. 

But  obviously  nothing  similar  can  occur  with  the  suc- 
cessive or  fusing  sensation-complexes  of  smell,  or  taste. 
Whatever  series  of  such  sensations  we  succeed  in  evoking 
in  consciousness  do  not  admit  of  "  easy,  frequent,  and 
rapid  repetition  in  varying  order  of  arrangement." 

The  case  of  the  ear,  however,  is  sometimes  contested. 
The  question  is  raised :  Why,  if  this  view  of  the  spatial- 
series  of  sensations  be  correct,  should  we  not  objectify  the 
different  tone-colors  as  lying  side  by  side  in  superficial  ex- 
tension, or  as  having  the  three  dimensions  which  belong  to 
objects  seen  and  touched  ?  The  objection  implied  in  this 
question  is  not  serious.  In  the  first  place,  the  ear  is  not, 
like  the  eye  and  the  hand,  a  movable  organ  usable  at  will  for 
the  exploration  of  an  object.  Moreover,  by  far  the  greater 


298  PHYSIOLOGICAL   PSYCHOLOGY. 

number  of  the  sensations  it  brings  to  us  consist  of  sudden 
shocks  of  noise  which  occur  to  interrupt,  as  it  were,  the 
continuous  flow  of  sensations  of  the  eye,  skin,  and  muscles. 
Sensations  of  musical  tone,  arranged  in  serial  order,  are 
relatively  very  rare.  Few  people  have  heard  frequently 
more  than  a  half-score  of  tunes.  And  even  such  series  of 
sensations  of  sound  do  not  shade  into  each  other;  or  at 
all  meet  the  conditions  of  the  very  point  we  are  arguing, 
—  viz.,  that  of  being  adapted  for  easy,  frequent,  rapid,  and 
varied  repetition. 

B.  Spatial  series  of  sensations  must  be  comparable  and 
associable  with  each  other.     In  the  use  of  the  eye,  graded 
series  of  sensations  of  color  and  light,  with  distinguishable 
differences  of  quality  and  quantity,  are  constantly  accom- 
panied by  similarly  graded  series  of  tactual  and  muscular 
sensations.     These  different  spatial  series  are  comparable 
and  associable  with  each  other.     The  visual  objects  per- 
ceived are  dependent  upon  such  qualities  as  possessed  by 
these  series  of  sensation-complexes.     So,  too,  the  different 
series  of  sensations  that  arise  from  the  simultaneous  irrita- 
tion of  connected  areas  of  muscle   and  skin  possess  the 
qualities  necessary  for  the  so-called  "  geometrical "  senses. 
In  particular,  in  forming  the  field  of  touch,  the  fact  that 
the  peripheral  parts  of  the  body  so  frequently  come  into 
contact  with  each  other,  is  of  great  significance.     Thus, 
two   series   of   sensation-complexes  corresponding   to  the 
perceptions  of  "  touching  "  and  "  being  touched  "  are,  as  it 
were,  brought  into  juxtaposition  in  consciousness.     This 
"  juxtaposition  "  is  not  itself  a  spatial  juxtaposition ;  but  it 
is  the  necessary  precondition  of  our  forming  the  perception 
of  the  object  as  consisting  of  parts  lying  side  by  side. 

C.  Spatial  series  of  sensations  must  be  differentiated  by 
the  possession  of  "local  signs"     It  has  already  been  said 
that  we  understand  by  a  "local  sign,"  that  peculiar  mix- 
ture or  shading  of  quality  which   belongs  to   sensations, 


PERCEPTION  SY  THE  SENSES.          299 

otherwise  qualitatively  alike,  on  account  of  the  particular 
locality  of  the  organ  to  which  the  stimulus  is  applied. 
Lotze,  the  originator  of  the  theory  of  local  signs,  con- 
ceived of  them,  in  the  special  case  of  the  eye,  in  the 
following  way.  In  addition  to  the  same  sensation  (for 
example,  red,  K)  which  each  color-tone  produces  at  all 
places  of  the  retina,  it  produces  also  an  "adjunct"  or 
"  accessory  "  impression,  a,  /3,  7,  etc.,  for  each  of  the  differ- 
ent retinal  places,  a,  b,  c,  etc.  The  nature  of  this  adjunct 
impression  for  the  different  places  of  the  retina  he  ex- 
plained as  follows :  When  the  image  of  a  luminous  point 
falls  upon  any  place  of  the  retina  lying  outside  of  the 
"  clear-spot "  of  vision,  we  instinctively  rotate  the  eye  in 
order  to  bring  this  image  upon  the  most  sensitive  spot 
of  the  retina.  Thus  a  series  of  changing  "feelings  of 
position  "  have  been  developed,  corresponding  to  each  arc 
through  which  the  eye  has  been  frequently  rotated.  To 
fixate  the  point  E,  rotation  has  taken  place  frequently 
through  arcs  corresponding  to  PE,  RE,  SE,  etc.  To  these 
arcs  of  rotation  correspond  the  "  feelings  of  position,"  TTC, 
pe,  ere,  etc. 

Now  when  two  or  more  points  of  the  retina,  lying  in 
different  directions,  are  simultaneously  stimulated, — for 
example,  P,  R,  S,  —  this  calls  into  consciousness  at  the 
same  time  all  the  "  feelings  of  position  "  corresponding  to 
the  arc  of  rotation  of  each  point. 

Objections  may  be  raised  to  Lotze's  view  of  the  nature 
of  the  so-called  "local  signs"  of  the  eye.  Especially  does 
the  term  "  adjunct  "  or  "  accessory  "  impression  seem  to  us 
unfortunate.  Nor  are  we  perfectly  sure  that  the  excited 
retinal  elements  do  not,  of  themselves  and  irrespective  of 
previous  movements  of  the  whole  eye,  have  a  peculiar 
value  in  consciousness.  But  the  assumption,  that  the 
different  minutest  distinguishable  areas  of  the  eye  and 
skin  have  attached  to  their  action  peculiar  shadings  in  the 


300  PHYSIOLOGICAL  PSYCHOLOGY. 

resulting  qualities  of  the  sensations  evoked,  seems  required 
for  the  construction  of  any  intelligible  theory  of  percep- 
tion. Moreover  —  as  we  shall  see  subsequently  more  in 
detail  —  the  same  assumption  also  seems  warranted  by  the 
facts. 

In  general,  then,  we  conceive  of  the  local  signs  in  the 
following  way:  The  irritation  of  the  different  elements 
of  certain  organs  of  sense  gives  rise  to  sensations  which 
differ  in  the  shading  of  their  quality,  according  to  the 
locality  in  the  organ  at  which  the  elements  are  situated. 
But,  especially  in  our  ordinary  experience,  the  irritation  of 
none  of  these  elements  takes  place  singly.  The  simulta- 
neous irritation  of  several  of  these  elements  results  then 
in  a  "  sensation-complex  "  ;  and  this  sensation-complex  is 
distinguished  from  all  other  most  nearly  similar  sensation- 
complexes,  by  a  peculiar  mixture  of  shades  of  quality 
dependent  upon  the  number  and  local  character  and  rela- 
tion of  all  the  elements  thus  simultaneously  irritated. 

For  example,  the  sensation-complex  aroused  by  irritating 
together  the  retinal  elements  a,  6,  c,  d,  etc.,  differs  from 
that  aroused  by  irritating  the  retinal  elements  5,  <?,  d,  £, 
etc.  The  same  thing  holds  true  of  locally  related  nervous 
elements  of  the  skin.  Indeed,  each  of  the  spatial  series  of 
sensations  is  characterized  by  a  kind  of  local  coloring  for 
its  different  sensation-complexes. 

The  foregoing  theory  is,  therefore,  opposed  to  that  of 
Bain  and  others  of  the  so-called  Associational  School,  who 
endeavor  to  reduce  all  local  signs  to  mere  symbols  of 
associated  differences  in  the  muscular  sense.  We  shall  see 
abundant  reason  for  holding  that  the  muscular  sense  has 
by  no  means  such  an  exclusive  position  as  the  theory  of 
this  school  would  indicate. 

One  other  important  consideration  remains.  The  local 
signs  of  the  different  spa'tial  series  evoked  in  the  use  of  a- 
very  complex  and  active  organ,  like  the  eye  or  the  hand, 


PERCEPTION  BY  THE  SENSES.  301 

must  necessarily  imodify  each  other.  Hence  there  arise 
admixtures  of  sensations  dependent  upon  the  fusion  of  the 
specific  energies  of  the  nervous  elements  simultaneously 
excited.  For  example,  the  place  where  we  locate  a  visual 
object  does  not  depend  merely  upon  the  place  where  its 
image  falls  upon  the  retina;  but  also  upon  the  "feelings  of 
position "  which  indicate  to  us  the  amount  and  direction 
of  the  turning  of  the  eye,  and  even  of  the  head,  neck,  and 
trunk  of  the  body.  Thus,  too,  is  our  perception  of  the 
position,  size,  shape,  etc.,  of  any  object,  when  located  in 
contact  with  the  skin,  dependent  upon  a  gross  mixture  of 
many  delicately  variable  sensation-complexes  belonging  to 
various  spatial  series.  The  complication  and  elaborateness 
of  experience,  and  the  niceness  and  variety  of  discrimina- 
tions, which  this  theory  implies,  will  be  no  obstacle  to  any 
student  of  the  mind  who  has  carefully  observed  and 
reflected  upon  the  phenomena. 

Indeed,  we  may  observe  our  own  sensations  in  a  way 
which  seems  to  give  the  warrant  of  immediate  intuition 
to  the  view  which  regards  them  as  infinitely  varied  in 
local  coloring.  Let  one  select  two  portions  of  the  body 
whose  structure  and  function  are  most  nearly  identical ; 
and  then  compare  the  sensation-complexes  called  out  by 
simultaneously  irritating  these  portions.  The  correspond- 
ing areas  on  the  tips  of  the  two  middle  fingers  will  fulfil 
the  necessary  conditions.  When  we  gently  rub  these 
finger-tips  together  (but  only  in  case  neither  is  too  widely 
differenced  from  the  other  by  some  peculiarity  of  structure 
or  use, — e.g.  by  a  callous  spot  or  something  similar),  the 
sensation-complexes  corresponding  to  the  terms  "touch- 
ing "  and  "  being  touched  "  seem  to  fluctuate  between  the 
two  fingers.  Either  finger,  accordingly,  can  at  will  be 
regarded  as  touching  or  as  being  touched.  Or,  perhaps, 
the  whole  sensuous  condition  evoked  almost  entirely  loses 
its  objective  reference,  and  seems  to  resemble  the  purely 


302  PHYSIOLOGICAL   PSYCHOLOGY. 

subjective  character  of  smells  or  sensations  of  musical 
tone. 

Under  ordinary  circumstances,  however,  the  two  sets  of 
spatial  series  evoked  by  bringing  two  areas  of  our  own 
bodies  into  contact  are  so  strongly  characterized  by  the 
local  signs  belonging  to  each,  that  we  have  no  choice  as 
to  which  member  shall  be  regarded  as  touching,  and  which 
as  being  touched.  For  example,  if  the  forehead  be  moved 
against  the  stationary  tip  of  a  finger,  the  character  of 
the  sensation-complexes  will  deceive  us  into  attributing 
motion  to  the  finger  rather  than  to  the  forehead.  The  tip 
of  a  finger  of  normal  sensitiveness  in  contact  with  the  tip 
of  a  callous  finger  is  determined  as  the  one  touching  some- 
thing ;  the  callous  finger  is  determined  as  a  part  of  our 
body,  being  touched.  Pricks,  hard  pressure,  pains,  sen- 
sations of  creeping  and  tickling,  we  locate  in  the  body. 
Indurated  spots  of  our  own  skin  we  regard  as  foreign 
substances.  In  general,  sensations  characterized  by  local 
signs  which  have  a  strong  and  decided  tone  favor  the 
process  of  localizing ;  sensations  of  a  toneless  kind  favor 
the  process  of  objectifying. 

(6)  "  Empiristic  "  and  "  Nativistic ' '  Theories. — Two  rival 
views  exist  as  to  the  explanation  of  the  nature  and  origin 
of  perception  by  the  senses.  They  have  been  called 
the  "  nativistic  "  (or  intuitional)  and  the  "  empiristic  "  by 
Helmholtz,  and  the  "  nativistic"  and  "genetic  "  by  Wundt. 
These  different  views  can  scarcely  be  spoken  of  as  opposed 
theories ;  they  are  better  described  as  the  result  of  tenden- 
cies which  appear  in  the  attitudes  assumed  by  two  classes 
of  observers  towards  two  classes  of  facts  and  towards  the 
explanation  of  the  facts.  Adherents  of  the  "  nativistic  " 
view  are  inclined  to  depreciate  the  explanations  offered  by 
the  empiricists,  as  to  how  and  why  our  perceptions  come  to 
have  the  character  they  actually  bear;  they  themselves 
prefer  to  emphasize  the  intuitional  and  underived  activity 


PERCEPTION  BY  THE  SENSES.  303 

of  the  mind.  But  adherents  of  the  "  empiristic  "  view,  on 
the  contrary,  are  inclined  to  admit  no  explanations  which 
refer  to  the  mind's  native  constitution  or  powers;  they 
prefer  to  fill  in  the  gaps  of  knowledge  with  explanations 
derived  by  conjecture  from  alleged  experimental  data. 

We  believe  that  certain  principles,  contended  for  by 
both  these  theories,  must  be  admitted.  The  right  to 
"  explain "  mental  phenomena,  by  giving  the  descriptive 
history  of  their  rise  and  development,  and  by  scientific 
statement  of  the  relations  they  uniformly  sustain  to  each 
other  and  to  phenomena  of  a  physical  order,  is,  of  course, 
beyond  question.  It  is  for  this  right  that  the  "  empiristic  " 
school  contend.  In  concession  to  this  view  it  must  be  ad- 
mitted that  the  "  immediateness  "  or  intuitional  character 
of  all  our  perceptions  is  illusory.  This  is  as  true  of  the 
art  of  seeing  and  touching  common  things,  as  it  is  of  the 
art  of  handling  a  graver's  tool  or  of  playing  upon  a  violin. 

On  the  other  hand,  the  ;i  empiristic "  theory  can  never 
so  far  perfect  its  explanations  as  rightfully  to  withhold 
from  the  mind,  considered  as  the  subject  of  the  psychical 
phenomena,  the  claim  to  possess  all  its  so-called  native 
powers.  The  elements  of  perception  are  psychical  factors, 
— sensations  and  sensation-complexes;  they  must,  there- 
fore, be  regarded  as  forms  of  the  mind's  reaction  on  occa- 
sion of  the  stimulation  of  the  nervous  centres  in  definite 
ways.  The  laws  of  the  synthesis  and  evolution  of  the  per- 
ception-products and  perception-processes  are  mental  laws, 
—  that  is,  constitutional  and  native  modes  of  the  behavior 
of  the  subject  which  we  call  mind.  Especially  is  it  true  of 
this  characteristic  of  "  space-form,"  which  belongs  to  all  the 
complex  products  of  perception  by  the  senses,  that  it  is  a 
subjective  and  mental  mode  of  arranging  and  regarding 
the  sensation-complexes.  Space-form  is  mental  form;  to 
impart  it  is  a  mental  achievement  which  implies  a  native 
character  to  the  mind. 


304  PHYSIOLOGICAL   PSYCHOLOGY. 

In  making  such  admissions  as  those  immediately  forego- 
ing, it  is  implied  that  we  have  reached  the  limits  of  scien- 
tific explanation  by  tracing  the  genesis  and  uniform  rela- 
tions of  the  phenomena.  But  such  limits  are  met  in  all 
attempts  at  scientific  explanation.  They  are  not,  indeed, 
to  be  arbitrarily  set  up,  nor  held  fixed  in  place  at  points 
beyond  which  scientific  research  has  succeeded  in  passing. 
But  their  existence  is  to  be  acknowledged  in  every  form 
of  science. 

Our  general  position  will  subsequently  receive  special 
illustration  in  the  case  of  the  eye.  It  is  over  the  theory 
of  perception  by  this  organ  that  the  "  nativistic "  and 
the  "  empiristic  "  views  are  most  warmly  debated.  Some 
investigators  conclude  that  perception  of  "extensity"  in 
three  dimensions  is  native  to  the  eye.  Others  would  limit 
this  native  power  of  the  eye  to  the  perception  of  extension 
in  two  dimensions.  Others  still  take  the  more  purely  "em- 
piristic "  position  and  contend  that  the  original  sensation- 
complexes  of  a  visual  order  have  no  spatial  qualities ;  they 
are  to  be  regarded  as  neither  "out"  nor  "spread-out,"  — 
whether  in  two  or  three  dimensions.  Yet  the  most  extreme 
"  empiristic  "  position  cannot  avoid  virtually  ascribing  to 
the  mind  the  native  power  to  have  and  to  combine  the 
sensation-complexes,  in  such  order  and  manner,  that  the 
perception  of  objects  in  three  space-dimensions  is  the  actual 
result  of  its  activity. 

The  theory  which  we  shall  now  illustrate  involves  the 
following  position  on  this  point :  Perception  is  an  achieve- 
ment due  to  extremely  complex  activities  of  the  psychical 
subject  —  the  Mind  ;  it  involves  the  synthesis  of  a  number  of 
sense-data  according  to  laws  that  are  not  deducible  from  the 
nature  of  the  external  objects,  or  of  the  physiological  action  of 
the  end-organs  and  central  organs  of  sense.  What  are  the 
laws,  or  uniform  modes  of  action,  followed  in  the  genesis 
and  development  of  perception  by  the  senses,  has  already 


PEKCEPTION  BY  THE  SENSES.          305 

been  somewhat  fully  stated.  The  subsequent  treatment  of 
the  particular  senses  will  explain  and  illustrate  them  more 
fully.  It  will  also  add  to  them  a  number  of  subordinate 
laws ;  and  it  will  indicate  how  far,  in  each  case,  the  "  em- 
piristic  "  and  the  "nativistic"  views  are  capable  of  scien- 
tific verification. 

It  must  constantly  be  borne  in  mind  that  the  scientific 
position,  as  psychology  takes  and  maintains  it,  regards  the 
nature  and  evolution  of  perception  as  a  subjective  affair.  It 
discards,  at  once  and  for  all,  the  so-called  "  common-sense  " 
point  of  view,  from  which  the  perceptions  are  regarded  as 
"copies"  or  "impressions"  of  things  having  a  ready-made 
and  eatfra-mental  existence.  Neither  is  its  point  of  view 
the  same  as  that  of  purely  physical  or  physiological  science. 
In  other  words,  we  investigate  the  genesis  and  development 
of  perceptions,  not  the  constitution  and  growth  of  material 
things.  But  since  we  are  considering  psychology  from  the 
physiological  point  of  view,  we  regard  this  genesis  and 
development  of  perceptions  as  determined  by,  and  con- 
ditioned upon,  the  activity  of  the  nervous  system  when 
excited  by  external  stimuli. 

PERCEPTION  BY  THE  "NON-GEOMETRICAL"  SENSES. 

A  certain  measure  of  perceptive  knowledge  of  things 
comes  to  us  indirectly  through  those  senses  which  have 
been  called  "  non-geometrical."  Strictly  speaking,  the 
knowledge  thus  gained  never  becomes  an  immediate  per- 
ception of  things.  The  rather  does  it  always  remain  an 
indirect  knowledge  about  things ;  but  about  things  which 
we  perceive  directly  through  the  "  geometrical "  senses 
so-called. 

Perceptions  of  Smell.  —  The  perceptions  of  this  sense 
differ  only  as  respects  fineness,  duration,  and  accompany- 
ing tone  of  feeling ;  they  have  neither  size  nor  shape,  nor 
spatial  properties  of  any  kind.  They  are  not,  as  sensation- 


306  PHYSIOLOGICAL   PSYCHOLOGY. 

complexes  purely  of  smell,  directly  localized.  They  are 
indirectly  localized,  however,  in  the  nose  and  surrounding 
parts  of  the  face,  by  the  tactual  and  muscular  sensations 
which  accompany  them. 

The  exploits  of  some  animals  give  ground  for  the  con- 
jecture that  every  species,  and  probably  every  individual 
animal,  has  an  odor  of  its  own.  From  our  own  experience 
we  know  that  different  smellable  objects  produce  character- 
istic sensations  of  smell.  In  this  indirect  way  we  are  said 
to  perceive  the  object  in  whose  effluvia  the  irritation  of  our 
end-organs  originates.  Its  distance  and  direction  are 
known  by  the  variations  in  intensity  and  quality  of  the 
sensations,  particularly  as  we  turn  the  head,  and  as  we 
advance  or  recede  in  one  direction  or  another.  In  case  of 
simultaneous  influence  from  two  smells,  the  stronger  over- 
whelms the  weaker.  We  cannot  hold  these  sensations  side 
by  side,  as  it  were,  even  by  means  of  the  tactual  and 
muscular  data  with  which  they  are  connected. 

Perceptions  of  Taste.  —  Since  the  tongue  is  the  chief 
organ  of  touch,  and  is  very  mobile  and  sensitive  to  pres- 
sure, sensations  of  taste  are  closely  connected  with  those  of 
touch.  In  themselves  considered  they  have  no  spatial 
qualities,  no  local  habitation. 

When  a  sour  mass  is  laid  on  one  half,  and  a  bitter  mass 
on  the  other  half,  of  the  tongue,  a  conflict  of  sensations 
takes  place.  We  may  determine  this  conflict,  under  cer- 
tain circumstances,  by  choice ;  but  we  cannot  place  the  two 
conflicting  sensations  side  by  side  in  consciousness.  When 
certain  tastes  compensate  each  other  —  as,  for  example, 
when  the  sugar  neutralizes  the  acid  of  the  lemon  —  it  is 
probable  that  the  compounding  of  the  two  effects  takes 
place  in  the  brain.  The  sensation  of  bitter  is  particularly 
difficult  to  cover  or  neutralize. 

Perceptions  of  Hearing.  —  We  know  that  we  hear  with 
the  ear,  chiefly  through  those  sensations  of  shock  to  the 


PERCEPTION  BY  THE  SENSES.          307 

muscles  and  skin  of  the  region  which  are  produced  by  loud 
and  massive  or  piercing  sounds.  Certain  acoustic  sensa- 
tions called  "  entotic  "  originate  through  excitement  within 
or  near  the  organ  itself ;  the  stimuli  of  these  sensations  are 
probably,  in  most  cases,  transmitted  through  the  tympanum. 
Thus  a  low  musical  tone,  due  to  the  vibration  of  the  adjoin- 
ing muscles,  may  be  heard  by  pressing  the  fingers  in  the 
ears  and  setting  the  teeth  tightly  together.  Yawning  may 
produce  a  cackling  noise ;  quinine  and  other  cerebral  exci- 
tants induce  ringing  or  singing  in  the  ears.  The  beating 
of  the  heart  and  the  whirring  of  the  blood  are  often  audible. 
The  localization  of  "  entotic  "  sounds  is  always  an  elaborate 
act  of  judgment,  and  is  often  extremely  perplexing.  In 
certain  pathological  cases  the  power  to  distinguish  between 
them  and  external  sounds  is  wholly  lost. 

We  orientate  ourselves  in  space,  with  reference  to  exter- 
nal sounds,  as  an  acquired  art,  differing  greatly  in  different 
individuals  and  dependent  upon  previous  experience  in  the 
use  of  the  senses  of  sight  and  touch.  The  data  on  which 
these  judgments  are  founded  are  only  partially  explored. 
It  appears  that  the  sensitiveness  of  the  skin  of  the  external 
meatus  and  of  the  tympanum,  as  well  as  the  position  and 
normal  direction  of  the  semi-circular  canals,  are  involved. 
Some  patients  with  anaesthesia  of  the  skin,  extending  to 
the  meatus  and  tympanum,  can  hear  perfectly  well  the  tick 
of  a  watch,  but  cannot  tell  on  which  side  of  the  head  to 
place  it  or  whether  the  sound  is  external  to  the  head  or 
not.  Recent  experiments  tend  to  show  that  possibly  the 
nerves  of  each  ampulla  have  a  specific  energy  in  localiza- 
tion. With  normal  ears,  right  and  left  are  rarely  confused ; 
but  positions  where  the  angle  made  by  the  direction  of  the 
sound  with  the  plane  of  two  canals  is  nearly  equal  are 
easily  confused.  Years  ago  Rayleigh  found  that  the  direc- 
tion of  a  tuning-fork  could  be  much  better  detected,  when 


308  PHYSIOLOGICAL  PSYCHOLOGY. 

held  to  the  right  or  to  the  left  of  the  head  than  when  held 
either  behind  or  before. 

Our  perceptions  of  the  absolute  distance  of  sounding 
objects  are  entirely  dependent  upon  our  knowledge  of  the 
quantity  and  quality  of  the  sounds  ordinarily  proceeding 
from  them.  It  may  be  that  a  change  in  timbre  aids  our 
perception  of  the  distance  of  a  musical  "  clang." 

Sensations  of  sound  appear,  therefore,  not  to  be  directly 
localized,  but  to  be  projected,  through  complicated  indirect 
inferences,  in  a  space  constructed  by  the  activity  of  the  eye 
and  the  hand.  The  utmost  that  could  be  claimed  would 
be  that  the  "sensations  of  position"  originating  in  the 
semi-circular  canals  have  become  so  fused  with  certain 
acoustic  sensations  as  to  constitute  a  kind  of  tact  which 
has  the  semblance  of  intuitive  perception.  Even  this 
fusion,  however,  we  believe  to  be  an  acquirement  depend- 
ent upon  our  perceptions  of  things  by  the  geometrical 
senses.  Hearing,  then,  belongs  among  the  non-geometrical 
senses. 

CONSTRUCTION  AND   USE  OF  THE  FIELD   OF  TOUCH. 

Every  account  of  the  process  by  which  a  Field  of  Touch 
is  constructed,  and  extended  objects  become  known  as  in 
contact  with  the  skin  at  definite  points  or  areas,  must  begin 
by  describing  the  data  which  the  mind  has  for  such  activity. 

Fineness  of  the  Skin's  Sense  of  Locality.  —  The  physiolo- 
gist E.  H.  Weber  first  established  a  rule  for  measuring 
accurately  the  fineness  with  which  different  areas  of  the 
skin  are  able  to  localize  objects  in  contact  with  them.  For 
this  purpose  he  made  use  of  the  two  points  of  a  compass, 
blunted  so  as  to  prevent  the  sensation  of  being  pricked. 
The  minimum  distance  at  which  these  two  points,  when 
applied  to  any  area,  could  be  felt  as  two  localized  sensations, 
was  the  measure  of  the  sensitiveness  of  that  area.  This 
distance  he  found  to  vary  from  about  1  millimeter  for  the 


PERCEPTION  BY  THE  SENSES. 


309 


tip  of  the  tongue,  2  for  the  volar  side  of  the  last  phalanx 
of  the  finger,  5  for  the  red  part  of  the  lips,  and  11  for  the 
cheek,  to  31  for  the  back  part  of  the  hand,  40  for  the  fore- 
arm, and  68  for  the  skin  of  the  middle  of  the  back,  and  of 
the  upper  arm  and  leg.  A  recent  investigation  with  the 
same  means  for  measurement  has  employed  the  "  method 
of  equivalents,"  -  —  that  is,  the  compass  points  were  placed 
4  or  more  lines  (1  line  =  2.256  mm.)  apart  on  the  fore- 
head; and  it  was  then  found  how  far  apart  the  points 
of  a  second  compass  must  be,  on  the  various  areas  of  the 
body,  to  give  a  sensation  of  equal  aperture.  The  numbers 
of  the  table  are  given  in  ratios  of  the  parts  compared. 


H    £ 

PI 

ft    . 

. 

« 

. 

ft  a 

5  g 

H 

2  S 

2    H 

o  2 

fr     M 

fc     0 

2  § 

S  2 

fc     OD 

§  3 

IB 

a  « 

<!     H      6 

03  f3 

w  s 

§  2 
0 

gg 

gg 

^g 

>!  g 

§g£ 

8  3 

ggg 

4  lines 

1.668 

1.0165 

0.972 

0.5 

1.051 

8     " 

1.353 

0.9763 

1.043 

0.982 

1.012 

1.0 

1.055 

12     " 

1.048 

0.996 

1.022 

1.5 

1.044 

16     « 

1.037 

0.989 

1.013 

2.0 

1.033 

20     « 

1.016 

0.985 

1.000 

2.5 

1.028 

24     " 

1.032 

1.003 

1.017 

3.0 

1.025 

Character  of  the  "  Sensation-circles."  —  The  areas  on  the 
surface  of  the  skin  within  which  the  foregoing  minimum 
distances  of  the  points  of  the  compass  are  felt  as  two,  are 
called  "  Sensation-circles."  They  have,  as  a  rule,  an  ellip- 
tical shape  with  their  long  axes  up  and  down.  Their 
variation  may  be  shown  by  the  following  experiment : 
Separate  the  points  of  the  compass  just  a  little  less  than 
is  necessary  for  their  being  felt  as  two  when  applied  to 
some  particular  area  (say  the  cheek)  and  then  cause  them 
to  travel  slowly,  without  changing  their  aperture,  over  other 
areas,  —  the  person  experimented  upon  being  blindfolded. 


310  PHYSIOLOGICAL   PSYCHOLOGY. 

The  points  will  appear  in  consciousness  to  separate  more 
and  more  as  the  more  sensitive  areas  are  traversed ;  and  they 
will  appear  to  come  nearer  together  again  as  the  less  sen- 
sitive areas  are  traversed.  The  sensitiveness  of  the  different 
areas  is  in  inverse  proportion  to  the  size  of  the  sensation- 
circles. 

The  same  principle  holds  when  the  entire  area  of  the 
sensation-circles  is  filled  up  so  as  to  make  a  continuum  of 
localized  sensations.  Thus  Weber  found  that  the  circular 
form  of  a  tube  of  1^  Parisian  line  in  diameter  could  be 
recognized  by  pressure  on  the  tip  of  the  tongue ;  while  on 
the  skin  of  the  abdomen  the  diameter  of  the  tube  must 
reach  3f  inch  before  its  form  was  recognizable.  The  same 
thing  can  be  shown  by  laying  rods  on  the  skin. 

Great  differences  exist  between  different  individuals 
with  respect  to  the  sense  of  locality  on  corresponding  areas 
of  the  skin.  Some  are  not  more  than  one-fourth  as  sensi- 
tive as  others.  This  sense  is  also  capable  of  rapid  culti- 
vation. In  a  few  hours  the  perceptive  power  of  some  areas 
can  be  more  than  doubled.  Such  growth  in  power  is  slower 
at  first  for  the  areas  not  in  ordinary  use ;  it  is  more  rapid 
for  those  accustomed  to  daily  use.  It  is  a  very  surprising 
discovery  that  practice,  exclusively  with  a  member  of  the 
body  on  one  side,  will  result  in  improving  the  correspond- 
ing member  of  the  other  side.  Thus  Volkmann  reduced 
the  minimum  perceivable  distance  with  the  tip  of  the 
finger  on  loth  hands  —  on  the  right  from  0.85  to  0.4,  and 
on  the  left  from  0.75  to  0.45  line  —  by  practising  exclu- 
sively with  the  left  finger. 

The  high  degree  of  fineness  for  certain  space-perceptions 
attained  by  some  blind  persons  is  well  known.  With  those 
of  normal  vision  some  parts  of  the  body,  especially  the  tips 
of  the  fingers,  are  capable  of  receiving  great  refinement  of 
cultivation.  But  one  experimenter  failed,  even  by  persist- 


PERCEPTION  BY   THE   SENSES.  311 

ent  education  for  an  entire  month,  to  reduce  the  obtuseness 
of  the  skin  of  the  back  more  than  by  about  one-fourth. 

Explanation  of  the  "  Sensation-circles  "  of  the  Skin,  —  The 
reason  for  this  marked  difference  among  the  different  areas 
in  the  general  field  of  touch  is  both  physiological  and  psy- 
chological. The  physiological  reason  is  not,  however,  very 
clear.  It  was  natural  at  first  to  assume  that  each  circle  is 
provided  with  one  nerve-fibre  only,  whose  terminal  expan- 
sion covers  the  entire  circle.  But  every  point  within  each 
circle  is  itself  sensitive,  and  the  circle  as  a  whole  may  be 
diminished  greatly  by  the  effect  of  practice.  Such  an  ex- 
planation, therefore,  will  not  hold.  Weber  himself  thought 
that  the  sensation-circles  all  contain  a  number  of  isolated 
nerve-fibres ;  and  that,  in  order  to  have  the  impression  of 
two  distinct  localized  sensations,  several  unexcited  fibres 
must  exist  between  the  two  excited  fibres. 

The  psychological  explanation  of  the  sensation-circles  of 
the  skin  accords  with  the  principles  already  laid  down  for 
all  perception  by  the  senses;  it  therefore  illustrates  and 
proves  those  principles.  These  circles  represent  the  spatial 
difference  between  the  points  at  which  stimulus  must  be 
applied  to  the  skin  in  order  that  the  difference  in  the  "  local 
coloring  "  of  the  different  resulting  sensations  may  be  "just 
observable."  The  "  local  signs  "  of  the  skin  are  complex 
mixtures  of  sensations  belonging  to  the  different  localities. 
As  such  they  are  dependent,  not  only  upon  unchanging 
anatomical  and  physiological  differences,  but  also  upon 
habit  and  upon  association  with  each  other  and  with  other 
spatial  series  of  sensations  belonging  to  the  same  organ. 

More  precise  description  of  the  causes  why  the  sensation- 
circles  —  or,  what  is  the  same  thing,  why  the  degrees  of 
the  fineness  of  local  perception  —  differ  so  greatly  for  dif- 
ferent parts  of  the  body's  surface,  would  include  the  follow- 
ing particulars.  The  skin  of  the  different  areas  varies  with 
respect  to  richness  in  nerve-fibres,  thinness,  and  so  sensitive- 


312 


PHYSIOLOGICAL  PSYCHOLOGY. 


ness  to  light  pressure,  and  character  of  the  support  and 
tension  it  receives  from  the  underlying  parts  of  fat,  muscle, 
tendon,  and  bone,  when  stretched  across  them.  The  rela- 
tive fineness  of  the  organ's  sense  of  locality  is  also  a  func- 
tion of  its  mobility.  Thus,  in  general,  the  power  of  locali- 
zation belonging  to  the  different  parts  of  the  arm,  from 
the  shoulder-joint  to  the  finger-tips,  increases  in  some  such 
proportion  as  the  movableness  of  its  different  parts. 

The  view  to  be  taken  of  the  nature  of  Weber's  "  sensa- 
tion-circles "  has  been  largely  changed  by  the  recent  experi- 
ments—  already  reported  (see  p.  237  f.)  —  of  Goldscheider 
and  others.  The  fineness  of  discrimination  possible  for 
any  area  of  the  skin  depends  largely  upon  how  all  the 
points  irritated  stand  related  to  the  specific  "pressure- 
spots  "  within  that  area.  Only  when  two  irritating  points 
touch  two  pressure-spots  are  they  felt  as  two.  The  impres- 
sion of  being  doubly  touched  may  be  excited  by  the  points 
of  the  compass  when  lying  much  nearer  together,  if  the 
pressure-spots  upon  which  they  rest  belong  to  two  dif- 
ferent chains  than  if  both  spots  belong  to  the  same  chain. 
The  minimum  distance  which  admits  of  perception  is  sur- 
prisingly reduced  by  selecting  pressure-spots  which  have  a 
first  rate  of  intensity ;  that  is,  from  which  the  chain  of 
such  spots  radiates,  or  at  which  it  makes  a  sharp  bend. 
How  much  the  table  of  least  observable  differences  can  be 
reduced  by  careful  experimenting  under  this  rule,  a  com- 
parison of  the  following  figures  with  those  given  by  Weber 
(see  p.  308  f .)  will  show :  — 


Part  of  the  body.  mm. 

Back 4-6 

Breast 0.8 

Forehead 0.5-1.0 

Cheek 0.4-0.6 

Nose  and  chin 0.3 

Upper  and  lower  arm    .    .  0.5-1.0 


Part  of  the  body.  mm. 

Back  of  hand 0.3-0.6 

1  and  2  phalanges  (volar)  .  0.2-0.4 
1  and  2  phalanges  (dorsal),  0.4-0.8 

Upper  leg 3.0 

Lower  leg 0.8-2.0 

Back,  and  sole  of  foot  .     .  0.8-1.0 


PERCEPTION  BY  THE  SENSES.          313 

When  an  area  of  the  skin  is  touched  with  any  object, 
even  so  small  as  the  blunted  points  of  the  compass,  a  large 
number  of  pressure-spots,  and  of  other  spots  of  specifically 
different  sensations,  are  simultaneously  excited.  The  result 
is  a  very  tangled  complex  of  sensations  fused  into  a  sensa- 
tion-complex, having  its  own  peculiar  local  coloring.  Sen- 
sations of  pressure  are  primarily  "  punctiform  "  ;  it  is  only 
as  they  are  massed,  and  fused  with  other  sensations,  that 
perception  of  a  tactual  continuum  results. 

The  ultimate  explanation  of  the  "  sensation-circles "  of 
the  skin,  as  regarded  in  the  light  of  the  most  modern 
researches,  forcefully  illustrates  and  confirms  the  theory 
of  perception  by  the  senses  which  was  stated  in  general 
form  at  the  beginning  of  the  present  chapter. 

The  construction  of  the  field  of  touch,  in  the  most  general 
meaning  of  the  words,  is  closely  connected  with  the  rise 
and  growth  of  another  form  of  perception  ;  we  refer  to  — 

Perception  of  Motion  by  the  Skin.  —  Different  parts  of  the 
surface  of  the  body  differ  greatly  with  respect  to  their 
power  of  discriminating  the  fact,  the  direction,  and  the 
amount  of  motion  in  contact  with  them.  Specific  "  sensa- 
tions of  motion  "  are  referred  to  by  some  writers  on  this 
subject.  We  believe  the  language  to  be  misleading.  Per- 
ception of  motion  depends  upon  the  successive  irritation  of 
the  organ  in  such  manner  that  the  local  coloring  of  the 
resulting  sensation-complexes  is  changed  with  the  right 
degree  of  rapidity.  These  sensation-complexes  fade  into 
each  other,  as  it  were,  after  a  manner  analogous  to  that  of 
the  fields  of  vision  when  we  slowly  turn  a  kaleidoscope 
before  the  eye. 

The  discriminative  sensibility  of  the  skin  for  motion  is 
much  greater  than  that  for  separate  touch  as  determined 
by  Weber's  experiments.  It  does  not,  however,  seem  too 
great  to  be  accounted  for  by  changes  in  local  coloring  as 
possible  in  accordance  with  the  more  recent  experiments. 


314  PHYSIOLOGICAL  PSYCHOLOGY. 

G.  Stanley  Hall  found  the  average  distance,  in  millimeters, 
which  a  metallic  point  could  move  over  the  skin  at  a  rate 
of  2  mm.  per  second,  before  a  judgment  of  direction  could 
be  securely  formed,  —  as  follows  :  forehead,  0.20 ;  upper 
arm,  0.40;  fore-arm,  0.44;  skin,  0.60;  palm,  0.74;  back, 
0.85. 

Motion  of  a  point  travelling  over  the  skin  can  be  pro- 
duced so  slowly  as  not  to  be  perceived  at  all,  even  after  two 
or  three  inches  have  been  actually  traversed.  Heavy  weights 
moving  at  the  same  rate  of  motion  as  light  weights  seem 
to  move  faster.  The  heat-spots  and  cold-spots  are  probably 
of  service  in  judging  the  rate  and  direction  of  motion. 
The  same  thing  is  true  of  sensations  of  deep  pressure,  when 
called  forth  in  combination  with  those  of  light  touch. 

Conclusions  from  the  foregoing  data  agree  admirably 
with  the  several  points  in  the  general  theory  of  perception 
which  have  already  been  proposed.  Our  perception  of 
moving  bodies  is  especially  keen  because  the  motion  does 
not  simply  multiply,  but  also  diversifies  our  data  for  filling 
up  the  dermal  blind-spots,  and  so  judging  the  nature  of 
impressions.  The  perception  of  each  locality  may  be  de- 
scribed as  based  upon  a  "  tangle  "  of  various  dermal  sensa- 
tions ;  for  the  dermal  "  local  signs  "  are  complex  mixtures 
of  sensations,  which  give  to  each  locality  a  characteristic 
local  stamp.  Our  ability  to  perceive  the  rate  and  direction 
of  motion  over  the  skin  depends  upon  the  degree,  quality- 
mixture,  and  rate,  of  the  changes  of  these  sensation-com- 
plexes. 

Localization  of  Temperature-Sensations.  —  In  all  our  ordi- 
nary perceptions  constructive  of  the  field  of  touch,  sensa- 
tions of  temperature  are  combined  with  those  of  light 
pressure  or  of  motion.  Recent  experiments  show  that  the 
minimum  distance  apart  at  which  two  cold-spots  or  heat- 
spots can  be  felt  as  two,  differs  greatly  for  the  different 


PERCEPTION   BY  THE   SENSES. 


315 


areas  of  the  body.     The  following  table  gives  the  results 
of  Goldscheider's  experiments,  in  millimeters :  — 


PART  OF  THE   BODY  EXPERIMENTED  WITH. 

COLD-SPOTS. 

HEAT-SPOTS. 

Forehead  cheek  and  chin 

0  8 

3    5 

Breast                     •          . 

2  0 

4-5 

1-2 

4-6 

Back   

1.5-2.0 

4-6 

Upper  arm   

1  5-^0 

2-3 

I^ower  arm                                               . 

2-3 

2-3 

Hollow  of  the  hand 

0  8 

2  0 

Back  of  the  hand,  and  upper  and  lower  leg 

2-3 

3-4 

It  will  be  seen  that  the  sense  of  locality  connected  with 
the  cold-spots  is  about  twice  as  fine,  as  a  rule,  as  that 
connected  with  the  heat-spots.  Although  the  temperature- 
sensations,  by  constituting  a  part  of  the  "local  mixture," 
probably  aid  in  the  perception  of  spatial  relations  by  the 
skin,  they  are  not  well  fitted  in  themselves  to  constitute 
a  so-called  "  spatial  series."  Whenever,  for  example,  any 
area  of  the  skin  is  stimulated  by  both  heat  and  cold  simul- 
taneously, and  at  points  too  near  together  to  be  discrimi- 
nated by  touch,  the  two  sensations  are  not  localized  as 
lying  side  by  side.  The  area,  on  the  contrary,  feels  as 
though  it  were  being  touched  alternately  with  a  hot  and 
a  cold  object;  that  is,  a  wavering  of  perception  takes 
place  similar  to  that  which  takes  place  in  a  so-called 
"strife  of  color-sensations."  Moreover,  if  we  bring  to- 
gether two  large  areas  of  the  skin,  that  differ  considerably 
in  temperature,  it  is  difficult  by  strict  attention  to  the  tem- 
perature-sensations alone,  to  tell  which  area  is  the  warm 
one  and  which  the  cool. 


316  PHYSIOLOGICAL  PSYCHOLOGY. 

ORIENTATION  OF  THE  BODY  IN  SPACE,  WITHOUT  SIGHT. 

How  our  perceptions  —  or  "  feelings,"  as  they  are  some- 
times called  —  of  the  position  of  our  own  bodies,  either  as 
wholes  or  with  respect  to  the  relations  of  the  different 
members,  are  connected  with  the  dermal  sensations,  has 
been  much  debated.  That  the  sensation-complexes  which 
have  just  been  described,  and  which  are  localized  in  the 
skin,  are  of  great  assistance  in  forming  these  perceptions, 
there  can  be  no  doubt.  Patients  afflicted  with  ansesthesia 
of  the  skin  have  great  difficulty  in  telling,  with  the  eyes 
closed,  in  what  positions  the  limbs,  thus  insensitive,  have 
been  passively  placed.  For  example,  we  are  told  of  one 
such  patient  that,  "  with  an  arm  elevated  by  a  weight  and 
pulley,  and  being  told  to  touch  his  knee,  he  felt  for  it 
about  his  shoulders." 

A  survey  of  the  entire  subject,  however,  convinces  us 
that  it  is  not  by  sensations  originating  in  the  skin  alone 
that  we  orientate  in  space  our  bodies,  whether  as  wholes 
or  with  respect  to  their  separate  members,  excluding  the 
guidance  of  perceptions  of  sight.  In  such  a  work  of 
orientation,  the  perception  of  the  position  of  the  limbs 
through  sensations  arising  in  the  conditions  of  the  joints, 
undoubtedly  plays  an  important  part.  Slow  movements  of 
the  limbs  with  short  excursions  can  sometimes  be  recog- 
nized by  anaesthetic  patients,  when  accompanied  by  pres- 
sure on  the  joints  ;  otherwise  not.  Passive  movements  of 
the  fingers,  or  other  members,  are  less  easily  recognized 
when  the  joints  have  been  rendered  insensitive  by  the 
faradic  current. 

In  addition  to  sensations  of  the  skin  and  joints,  two 
other  classes  of  sensations  have  much  to  do  with  the  per- 
ception of  the  space-relations  of  our  bodies,  —  excluding 
sight. 

Perceptions  of  the  Muscular  Sense.  —  Three  views  have 


PERCEPTION  BY  THE  SENSES.          317 

been  held  as  to  the  character  and  service  in  perception  of 
those  sensations  which  are  attributed  to  the  muscle's  of  the 
body.  One  of  these  views  denies  that  specifically  muscular 
sensations  exist;  the  sensations  that  go  by  this  name  it 
attributes  to  the  skin  as  influenced  by  the  changes  of  ten- 
sion in  it,  when  the  underlying  muscles  are  moved.  An- 
other view  (that  of  Wundt)  resolves  these  sensations,  so 
far  as  they  are  not  tactual,  into  "  central  feelings  of  inner- 
vation,"  which  differ  only  in  intensity,  and  not  in  specific 
quality,  and  which  result  from  changes,  initiating  move- 
ment of  the  body  and  its  members,  that  take  place  in  the 
brain  as  correlated  with  acts  of  will.  The  third  view 
(which  we  advocate  for  reasons  already  referred  to  in 
part)  maintains  the  existence  of  muscular  sensations  as 
important  factors  in  those  "  spatial  series "  of  sensations 
whose  data  are  necessary  for  our  perception  of  the  chang- 
ing relations  of  our  body  and  its  members,  to  one  another 
and  to  other  objects,  in  space. 

It  has  already  been  said  (p.  242),  we  may  derive  a  cer- 
tain support  for  this  view  from  an  appeal  to  consciousness. 
In  moving  any  limb,  or  in  changing  the  posture  of  the 
entire  body,  attention  enables  us  in  a  measure  to  separate 
from  the  sensation-complexes  of  the  skin  and  joints,  other 
changes  in  sensation  which  we  localize  in  the  deeper  parts 
of  the  flesh.  As  the  circuit  of  motion  gone  through  by 
any  limb  increases,  or  the  intensity  of  the  strain  upon  the 
muscles  becomes  greater,  the  quality  of  the  mass  of  result- 
ing muscular  sensations  is  perpetually  changing.  Every 
one  who  has  called,  by  unusual  exercise,  upon  the  unused 
and  more  deeply  lying  muscles  of  the  body,  knows  what 
surprises  (consisting  of  qualitatively  new  masses  of  sensa- 
tions, as  it  were)  are  the  resulting  response  of  conscious- 
ness. 

Moreover,  experiment  and  pathology  tend  to  confirm 
the  impression  derived  from  attention  to  the  phenomena 


318  PHYSIOLOGICAL   PSYCHOLOGY. 

of  consciousness.  They  show  that  the  power  of  perceiv- 
ing the  position  and  movement  of  the  body  and  its  mem- 
bers does  not  vary  directly  and  solely  as  the  sensitiveness 
of  the  skin  and  joints.  The  superior  discriminating  power 
which  any  limb  acquires,  as  soon  as  it  is  permitted  to  move 
over  the  object,  and  to  explore  it  with  the  moving  limb,  is 
due  to  the  series  of  muscular  sensations  thus  evoked. 
When,  for  example,  we  trace,  with  the  same  spot  of  the 
fore-finger,  and  with  eyes  closed,  the  outline  of  an  unknown 
object,  it  is  the  direction  and  amount  of  motion  of  the  arm, 
as  known  by  the  series  of  muscular  sensations,  which  is 
chiefly  helpful  in  constituting  this  series  of  perceptions. 
In  all  active  touch,  whether  over  small  or  large  areas  of 
body,  however,  this  series  of  muscular  sensations  consti- 
tutes, with  the  dermal  sensations,  a  sort  of  double  system 
of  local  signs.  Hence,  as  the  experiments  of  Hall  and 
others  show,  our  judgment  of  the  direction  of  motion, 
even  when  the  body  is  itself  motionless,  is  prompter,  if 
the  weight  resting  on  the  skin  and  moving  is  increased  up 
to  the  limit  when  other  disturbing  sensations  intervene. 
Recent  experiments  seem  also  to  show  that,  in  estimating 
the  weight  of  bodies  lifted,  when  they  cannot  be  seen,  the 
judgment  is  much  influenced  by  the  speed  with  which  the 
weight  comes  up.  If  the  motor  discharge,  which  is  calcu- 
lated to  be  adjusted  to  the  raising  of  any  particular  weight, 
meets  with  unexpectedly  little  or  unexpectedly  great  re- 
sistance, and  the  weight  rises  with  unaccustomed  velocity, 
very  singular  illusions  may  result.  Of  course,  our  per- 
ception of  the  speed  with  which  the  weight  rises  is  com- 
plex, and  depends  upon  a  variety  of  peripherally  arising 
sensations. 

Perception  by  the  Semi-circular  Canals.  —  Recent  experi- 
ments seem  to  settle  beyond  doubt  the  influence  of  sensa- 
tions originating  in  irritation  of  the  semi-circular  canals 
upon  the  sense  of  direction,  —  at  least,  in  the  case  of  some 


PERCEPTION  BY  THE  SENSES.  319 

animals.  All  three  canals  have  now  been  separately  excited 
by  the  electrical  current,  and  the  direction  of  the  resulting 
motion  seems  to  be  specific  for  each  one  of  the  three.  It  is 
highly  probable  that  these  same  organs  in  man  are  closely 
connected  with  the  perceptions  by  which  he  fixes  the  posi- 
tion and  motion  of  his  body  and  of  its  members  in  space. 
Precisely  what  is  the  character  and  the  amount  of  this 
influence  physiological  psychology  is  not  as  yet  in  a  posi- 
tion to  affirm. 

We  cannot  proceed  much  farther  in  this  direction  for 
the  confirmation  and  illustration  of  the  general  theory  of 
perception,  without  introducing  the  case  of  the  eye.  But 
it  rs  probable  that  in  orientating  ourselves  with  closed  eyes, 
whether  we  remain  at  rest  or  are  in  motion,  an  important 
difference  exists  between  what  have  been  called  the  "  star 
tic  "  and  the  "  dynamic  "  perceptions  and  illusions.  When, 
for  example,  the  head  is  twisted  to  one  side,  with  closed 
eyes,  the  errors  in  our  attempt  to  localize  are  such  as  to 
show  that  "static  sensations  of  direction"  come  through 
the  muscles  of  the  eyes.  On  the  other  hand,  the  so-called 
dynamic  sensations  produced  by  rotating  the  body  are 
largely  due  to  variations  in  the  endolymph  pressure,  as 
the  head  is  turned  around  its  various  axes. 

Indeed,  the  knowledge  of  the  positions  of  our  bodies 
and  their  members,  even  as  gained  without  perceptions  of 
sight,  is  a  very  complicated  affair.  It  depends  on  several 
kinds  of  dermal  sensations,  on  sensations  of  the  joints, 
tendons,  etc.,  on  muscular  sensations,  and  on  sensations 
of  general  sensibility  appreciating  the  gravitation  of  fluids 
and  the  relation  of  internal  organs  of  the  body. 

In  the  development  of  this  kind  of  knowledge,  the 
activity  of  the  hand,  as  it  moves  over  or  lies  upon  the 
various  surfaces  of  the  body,  is  especially  important.  It 
constantly  carries  with  it,  as  it  were,  the  two  great  series 


320  PHYSIOLOGICAL   PSYCHOLOGY. 

of  combining  and  separating  and  re-combining  sensation- 
complexes  of  the  spatial  order,  —  namely,  sensation-com- 
plexes of  the  skin  and  those  of  the  muscles. 

The  localization  of  certain  fixed  and  characteristic  parts 
of  the  general  area  of  the  body,  that  have  marked  local 
characteristics  and  frequently  recur  in  experience,  is  a 
prime  achievement  in  the  construction  and  use  of  the  field 
of  touch.  To  these  landmarks,  as  it  were,  other  points  or 
areas,  subsequently  discovered,  are  referred.  One  hand 
learns  to  know  the  other ;  the  right  hand  chiefly  explores 
the  left  arm  and  side  and  the  upper  right  leg;  the  left 
hand,  the  right  arm  and  side  and  upper  left  leg.  The 
finger-tips,  especially  of  the  right  hand  (and,  in  the  infant's 
case,  the  lips),  have  an  office  to  perform  similar  to  that  of 
the  retina:  they  are  the  centre,  or  hearth,  of  clear  per- 
ceptions of  touch.  But  in  order  to  bring  them  to  their 
object  they  must  be  moved:  through  this  motion  fresh 
combinations  of  muscular  and  tactual  sensations  result. 
In  marked  contrast  with  these  active  and  discriminating 
organs  of  the  body  stand  certain  parts  of  the  surface  which 
are  known  to  us  at  all  only  as  they  are  clumsily  excited 
to  undiscriminating  responses  by  the  pressure  of  our  cloth- 
ing or  of  the  burdens  temporarily  in  contact  with  them. 

But  long  before  the  field  of  touch  has  been  constructed 
with  any  considerable  approach  to  completeness,  the  eye 
has  already  explored  those  parts  of  the  body  which  are 
open  to  its  inspection.  It  learns  first  to  know  the  hand, 
which  nature  keeps  constantly  in  motion  before  it.  As 
objects  excite  tactual  sensations  by  resting  on  the  hand, 
or  muscular  sensations  by  being  handled,  the  eye  is  also 
active  in  such  a  way  as  to  combine  these  two  classes  of 
sensations  with  visual  sensation-complexes.  Very  early  in 
the  development  of  the  perceptive  power,  it  comes  to  be 
the  leader  and  critic  of  the  discriminations  connected  with 
most  of  the  tactual  and  muscular  sensations.  Its  power 
of  rapid  movement  over  the  whole  field,  its  delicate  judg- 


PERCEPTION  BY  THE  SENSES.          321 

ment  011  account  of  the  finely  shaded  complex  local  signs, 
which  its  activity  calls  forth,  give  it  a  marked  superiority 
as  a  "  geometrical "  sense.  For  this  reason,  one  born  blind 
can  never  attain  the  same  "comprehensive  simultaneous- 
ness  "  for  his  perceptions  of  the  spatial  relations  and  spatial 
qualities  of  his  own  body  or  of  other  objects. 

Among  the  interesting  complex  perceptions  which  result 
from  the  habitual  synthesis  of  dermal  and  muscular  sensa- 
tion-complexes, are  the  so-called  — 

"Feelings  of  Double  Contact,"  — It  is  by  means  of  these 
perceptions  that,  exclusive  of  the  influence  of  sight,  skill 
is  acquired  in  the  use  of  tools,  weapons,  and  musical  instru- 
ments. In  such  cases,  the  process  of  eccentric  projec- 
tion (coupled  with  localization)  goes  so  far  that  we  feel 
the  object  with  which  the  implement  is  in  contact,  not  so 
much  in  the  hand  as  in  the  implement  itself,  as  though  it 
were  actually  a  part  of  our  sentient  organism.  The  wood- 
carver  feels  his  chisel  move  through  the  stuff  he  is  shaping. 
He  guides  it  as  unerringly  as  the  violinist  guides  his  finger, 
so  as  to  lay  the  tool,  with  a  given  degree  of  pressure  upon 
a  given  spot.  Such  management  is,  of  course,  made  possi- 
ble only  by  delicate  changes  in  the  local  coloring  of  the 
tactual  and  muscular  sensation-complexes,  as  the  move- 
ment of  the  handle  of  the  tool,  in  and  with  the  hand,  is 
variably  related  to  the  surface  of  the  skin  and  underlying 
muscles. 

Perceptions  of  this  sort  are  attained  through  a  more 
artificial  and  elaborate  process  of  localization.  -  As  skill 
grows,  they  become  perceptions  of  the  texture  or  condition 
of  a  comparatively  remote  external  object,  through  an 
organ  or  instrument,  instead  of  perceptions  of  the  condi- 
tion of  our  own  bodily  members.  The  relation  of  these 
"  feelings  of  double  contact "  to  our  estimate  of  our  own 
personality,  to  our  pleasure  in  extending  the  sphere  of  the 
mind,  as  it  were,  has  been  discussed  by  Lotze  in  an  inter- 
esting way. 


CHAPTER   XIV. 

PERCEPTION  BY   THE   SENSES.  — Continued. 

THE  most  wonderful  and  complex  of  all  the  organs  of 
perception  is  the  human  eye.  Nature  has  equipped  it  with 
superior  means  for  furnishing  to  the  mind  a  variety  of  data, 
as  respects  both  quantity  and  quality,  for  the  nicest  dis- 
criminations. It  reaches  a  very  high  degree  of  psychical 
development  very  early  in  life.  For  these  and  other 
reasons  it  is  peculiarly  difficult  to  give  a  complete  and 
satisfactory  account  of  those  sensation-complexes  which 
originate  through  its  activity,  and  of  the  laws  of  their 
combination  and  elaborating.  No  less  than  eight  different 
data,  or  motifs,  are  assigned  by  one  authority,  as  used  in 
adult  monocular  vision  for  the  perception  of  the  third 
dimension  of  space.  In  stereoscopic  vision  with  both  eyes 
in  motion,  at  least  two  other  very  complicated  series  of 
sensations,  of  "  spatial "  character,  must  be  added  to  this 
number. 

The  Empiristic  and  the  Nativistic  theories  of  perception 
find  their  principal  grounds  of  contention  over  the  case  of 
the  eye.  The  questions  about  which  they  contend  may  be 
essentially  reduced  to  this  :  How,  and  at  what  stage  in  the 
development  of  perception  by  the  eye,  do  the  visual  sensa- 
tions attain  the  so-called  quality  of  "  extensity  "  (or  big- 
ness), as  distinguished  from  intensity  and  color-tone  ? 
Several  of  the  data  enumerated  in  the  above-mentioned  ten 
classes,  are  of  only  secondary  rank  and  value.  Thus  much, 
however,  seems  necessary  to  the  most  elementary  form  of 
visual  perception  :  Sensations  of  light  and  color,  differing  in 
322 


PERCEPTION  BY  THE  SENSES.  323 

intensity  and  quality,  but  simultaneously  present  in  con- 
sciousness, must  be  systematically  ordered  by  the  help  of 
local  signs  of  the  retina,  and  associated  with  other  spatial 
series  of  muscular  sensations  arising  from  accommodation  of 
the  eye  and  from  its  motion. 

The  Two  Eyes  as  One  Organ,  —  The  complexity  of  the 
combinations  arising  in  the  case  of  the  eye  is,  of  course, 
greatly  increased  by  the  fact  that  there  are  two  eyes  acting 
as  one  organ.  Thus  there  are  two  sets  of  certain  data  to 
consider :  for  example,  two  systems  of  retinal  signs ;  two 
images  of  each  object;  two  sets  of  motion  in  accommoda- 
tion, and  in  convergence  and  divergence  of  the  axes.  The 
two  eyes  are,  however,  one  organ  of  vision  in  such  a  sense 
that,  even  when  one  eye  is  closed,  the  perceptions  of  the 
open  eye  are  irresistibly  influenced  by  sensations  originat- 
ing in  the  condition  arid  action  of  the  closed  eye.  The 
two  eyes  act  separately  in  such  manner  that  they  are  not 
one  organ  as  the  two  nostrils  or  two  ears  are  one ;  but 
they  act  together  in  such  manner  that  they  are  more  truly 
one  organ  than  are  the  two  hands.  We  shall  have  fre- 
quent occasion  to  notice  gaps  or  errors  in  certain  theories 
of  perception,  which  are  occasioned  by  neglecting  the  in- 
fluence of  one  of  the  two  members  of  this  double  organ  of 
vision. 

Method  of  Discussion  to  be  followed.  —  It  is  not  possible 
to  trace  the  development  of  visual  perception  by  an  appeal 
to  memory  or  imagination.  Neither  are  the  experimental 
data  sufficient  to  fill  up  all  the  gaps  left  in  consciousness. 
We  can  only  hope  to  disentangle  the  more  important  ele- 
ments from  that  complexity  of  elaboration  which  they  have 
attained  in  experience;  and  then  try  to  reconstruct  into  a 
consistent  theory  the  elements  thus  gained  by  analysis. 
In  pursuing  this  course  it  is  most  convenient  and  effective 
to  follow,  as  far  as  possible,  the  order  of  nature.  We  thus 
find  three  stages  of  complexity  and  growth,  as  it  were, 


324  PHYSIOLOGICAL  PSYCHOLOGY. 

which  need  explanation.  These  are :  (1)  The  retinal  image 
of  the  eye  at  rest  and  the  sensation-complexes  which  enter 
into  it;  (2)  the  single  eye  as  moved,  and  the  influence 
of  these  movements ;  (3)  the  conditions  furnished  by  the 
existence  and  relations  of  two  eyes  as  active  together. 

Corresponding  to  the  three  sets  of  considerations  just 
mentioned  we  may  speak  of  three  fields  of  vision,  in  the 
order  of  their  relative  complexity.  These  are:  (1)  The 
retinal  field  of  vision,  (2)  the  field  of  monocular  vision, 
and  (3)  the  field  of  binocular  vision.  By  the  first  we 
mean  that  spatial  arrangement  of  sensations  of  light  and 
color,  as  points  lying  side  by  side,  which  is  due  to  the 
excited  expanse  of  the  nervous  elements  constituting  the 
retina,  and  acting  without  motion  of  the  eye.  The  field 
of  monocular  vision  includes  all  that  can  be  seen  by  one 
eye,  unaided  and  uninfluenced  by  the  action  of  the  other 
eye ;  while  the  field  of  binocular  vision  includes  all  that 
can  be  seen  by  both  eyes. 

Experimentally,  we  cannot  construct,  in  the  case  of  one 
who  has  had  a  developed  experience  of  sight,  any  so-called 
"  field  of  vision  "  which  shall  be  irrespective  of  the  exist- 
ence and  motion  of  both  eyes.  We  may,  however,  apply 
our  analysis  to  the  supposed  cases  of  a  retinal  field,  and 
also  of  a  purely  monocular  field,  in  order  to  reconstruct  theo- 
retically the  process  by  which  the  mind  attains  perception 
with  two  active  and  experienced  eyes,  constituting  one  organ 
of  vision. 

The  "  Retinal  Field  "  of  Vision.  —  Let  us  close  or  blindfold 
both  eyes,  keep  them  as  motionless  as  possible,  and  allow- 
ing time  for  all  the  after-images  to  die  away,  await  the 
result.  We  shall  soon  perceive  a  mass,  or  "  extensity,"  of 
light  and  color  sensations,  projected  somewhat  indefinitely 
in  front  of  us.  Some  would  describe  this  extensity  of 
visual  sensations  as  felt  rather  than  seen.  Within  the 
entire  expanse  we  can  perhaps,  strictly  without  the  slight- 


PERCEPTION  BY  THE  SENSES.  325 

est  motion  of  the  eye,  localize  an  indefinite  number  of 
minute  points  of  color  and  light,  lying  side  by  side.  This 
expanse  of  visual  sensations  has  no  fixed  and  well-defined 
outline,  however ;  nor  can  we  localize  any  of  its  principal 
parts,  —  upper  right-hand,  lower  left-hand,  upper  centre, 
etc.,  —  without  making  minute  excursions  with  both  eyes. 
If  we  turn  the  face  upward,  the  "extensity"  of  visual 
sensations  is  now  above  us ;  if  we  turn  the  face  downward, 
it  sinks  toward  our  feet.  It  has,  indeed,  a  certain  seeming 
of  depth ;  its  appearance  is  not  that  of  a  darkly  colored 
wall  or  curtain  placed  close  before  the  eye.  But  this  seem- 
ing of  depth  is  largely,  if  not  wholly,  due  to  the  constant 
change  in  the  color-tone  and  brightness  of  the  minute 
portions  of  the  field,  which  has  an  effect  somewhat  like 
that  we  get  on  looking  at  a  very  dense  mist  of  particles 
differently  colored  and  drifting. 

It  is  perfectly  plain  that  most  of  this  perception  of  the 
locality  of  our  visual  extension  is  the  result  of  acquired 
skill.  Its  position  with  reference  to  the  entire  body  implies 
familiar  and  complex  tactual  and  muscular  sensation-com- 
plexes which  have  been  accustomed  to  assure  us  of  the 
position  of  the  body  and  its  members.  When  the  field 
ascends  or  descends,  for  example,  we  can  only  make  it 
seem  so  by  producing  in  the  neck  the  necessary  "  feelings 
of  position."  It  would  not  be  at  all  out  of  place  to  say 
that  we  then  "  see  "  this  retinal  field,  above  or  below,  with 
our  necks. 

Further  experiment  with  the  so-called  "retinal  field" 
serves  to  show  us  how  complicated  its  character  really  is ; 
and  how  much  of  accumulated  experience  and  skill,  won 
in  the  process  of  localizing  a  great  variety  of  sensation- 
complexes,  its  perception  involves.  For  example,  a  "  phos- 
phene "  produced  in  either  eye  changes  the  character  of 
the  entire  field.  Or  if  one  eye  be  opened,  the  "retinal 
field  "  of  the  closed  eye  is  at  once  submerged  in  the  objects, 


326  PHYSIOLOGICAL   PSYCHOLOGY. 

whose  position,  magnitude,  and  spatial  relations  belong  to 
the  "  monocular  field  "  of  the  open  eye.  Here  again,  how- 
ever, this  field  of  the  open  eye  can  be  drowned  in  a  shower 
of  sparks  caused  by  producing  a  strong  phosphene  in  the 
field  of  the  closed  eye. 

In  general,  it  will  be  found  that  the  extent  of  the  retinal 
field,  and  the  localization  of  the  whole,  as  well  as  of  its 
separate  parts,  are  dependent  upon  the  accommodation  and 
motion  of  both  eyes.  The  explanation  of  these  facts  would 
seem  to  necessitate  the  conclusion  that  the  perception  of 
position  and  of  localized  areas,  even  in  the  two-dimensioned 
retinal  field,  depends  upon  the  revival  of  associated  and 
already  localized  tactual  and  muscular,  as  well  as  visual, 
sensation-complexes. 

Immediate  Spatial  Form  of  Visual  Sensations.  —  On  grounds 
like  the  foregoing,  the  advocates  of  the  empiristic  view  (for 
example,  Wundt)  are  led  to  the  claim :  "  Our  sensations 
of  light  do  not  immediately  possess  spatial  form."  On  the 
other  hand,  various  forms  of  the  nativistic  view  insist  that 
"we  have  native  and  fixed  optical  space-sensations"  (so 
Professor  James).  In  our  judgment,  science  has  as  yet 
no  perfectly  certain  means  for  deciding  in  favor  of  either 
of  these  claims.  Experiment  and  observation  certainly 
show  that  almost  all  of  the  perceptive  value,  and  asso- 
ciated perceptive  influence,  which  changes  in  sensations 
possess  through  activity  of  the  eye,  is  acquired  in  the 
development  of  experience.  We  are  warranted  in  affirm- 
ing that  the  infant  has  no  original  visual  intuition  of  the 
space-qualities  and  space-relations  of  anything,  even  includ- 
ing the  members  of  its  own  body. 

The  ultimate  question  is,  however,  capable  of  statement 
in  some  such  form  as  follows :  When  a  number  of  the  reti- 
nal elements  are  simultaneously  irritated,  without  motion 
of  the  eyes,  do  the  resulting  sensation-complexes  of  light 
and  color  originally  possess  the  quality  of  "  extensity,"  — 


PERCEPTION  BY  THE  SENSES.          327 

whether  in  two  or  three  dimensions  ?  The  problem  pro- 
posed in  this  question  is  theoretical.  No  such  irritation 
probably  results  in  sensations  of  light  and  color  without 
accompanying  accommodation,  and  parallel  or  converging 
or  diverging,  movements  of  the  organ.  But  would  the 
resulting  sensation-complexes  possess  this  quality  of  exten- 
sity,  in  case  they  were  not  accompanied  in  the  earliest 
development  by  tactual  and  muscular  sensations  ?  The 
question,  we  have  already  said,  does  not  as  yet  admit  of 
a  perfectly  unequivocal  answer. 

It  should  be  said,  however,  in  favor  of  the  nativistic 
view,  to  some  extent  at  least,  that  the  mosaic  structure  of 
the  retina  suggests  the  eye's  native  perception  of  spatial 
form.  The  value  of  this  structure  for  the  development  of 
visual  perception  can  scarcely  be  understood  at  all,  unless 
the  irritation  of  each  minute  area  of  the  nervous  elements 
is  represented  by  a  local  sign,  or  shading  of  the  resulting 
sensation-complexes,  in  consciousness.  Moreover,  the  spa- 
tial discrimination  of  which  the  eye  is  capable  seems  too 
great  to  be  accounted  for  by  changes  in  muscular  sensation 
produced  by  accommodation  and  rotation  on  its  axes.  On 
the  contrary,  the  limits  of  discrimination  possible  by  per- 
ception with  the  eye  correspond  almost  exactly  with  the 
limits  of  the  retinal  structure  (see  p.  255). 

For  the  foregoing  and  other  reasons  we  are  inclined  to 
hold  that  spatial  perception,  though  at  most  in  very  incho- 
ate and  indefinite  form,  is  native  to  the  mind  as  a  synthesis 
of  the  qualitatively  different  sensations  which  result  from 
stimulating  simultaneously  the  retinal  mosaic  of  nervous 
elements. 

THE  CONSTRUCTION  OF  THE  FIELD   OF  VISION. 

The  spatial  form  assumed  by  those  sensations  which  are 
evoked  by  simultaneous  stimulation  of  many  retinal  ele- 
ments is,  however,  only  one  among  several  factors  neces- 


328 


PHYSIOLOGICAL   PSYCHOLOGY. 


sary  in  the  construction  of  a  "field  of  vision."  Vision, 
indeed,  in  any  sense  of  the  word  appropriate  to  the  adult 
organ,  involves  a  development  of  experience  with  moving 
eyes.  The  consideration  of  the  simplest  case  requires  that 
we  should  refer  to  the  physiology  of  the  eye.  Only  one 
small  spot  of  the  retina  (the  "  fovea  centralis  ")  is  capable 
of  giving  a  clear  image  of  an  object.  When  we  desire  to 
see  an  object  clearly  we  bring  its  image  upon  this  spot  and 
fixate  it  there.  The  point  of  the  object  which  corresponds 
to  the  point  of  the  image  falling  upon  this  spot  is  called 
the  "point  of  regard"  (sometimes  "fixation-point").  In 
ordinary  vision  the  complete  perception  of  the  object  in- 
volves the  rapid  and  constant  change  of  this  point  of 
regard. 

Rotation  of  the  Eye-ball.  —  The  wandering  of  the  point 
of  regard  over  an  object  may  be  considered  as  accomplished 

by  rotating  the  eye  upon  a 
pivotal  point,  or  centre  of 
rotation,  by  motions  that 
have  different  axes  of  ro- 
tation. This  point  is  really 
a  minute  interaxial  space, 
located  about  1.24-1.77 
mm.  behind  the  middle  of 
the  optical  axes.  There 
are  three  axes  to  be  distin- 
guished, —  an  antero-pos- 
terior,  a  vertical,  and  a 
transverse.  About  these 
axes  the  six  muscles  (see 
p.  81)  variously  turn  the 
eye,  —  one  only  being 
needed  for  movements  in- 
ward and  outward,  two 
for  movements  upward  and  downward,  and  three  for  com- 


r/ext.  r.  inf.  r.  int. 


FIG.  79.  — Diagram  of  the  Attachments  of 
the  Muscles  of  the  Eye,  and  of  their  Axes  of 
Rotation  — the  latter  being  shown  by  dotted 
lines.  The  axis  of  rotation  of  the  rectus,  ex- 
ternus,  and  internus,  being  perpendicular  to 
the  plane  of  the  paper,  cannot  be  shown. 


PERCEPTION   BY   THE   SENSES.  329 

bined  movements  of  inward  or  outward  with  upward  or 
downward. 

A  line  drawn  from  the  centre  of  rotation  to  the  point  of 
regard  is  called  the  "  line  of  regard."  Such  a  line  may  exist, 
of  course,  for  each  eye.  A  plane  passing  through  the  two 
lines  of  regard  is  called  the  "  plane  of  regard."  When  the 
head  is  erect  and  the  line  of  regard  directed  toward  the 
horizon,  the  eyes  are  said  to  be  in  the  "primary  position." 
Rotations  of  the  eye,  without  torsion,  may  be  regarded  as 
movements  of  the  eye  upon  its  transverse  and  vertical  axes. 
Rotation  of  the  transverse  axis  displaces  the  line  of  regard 
either  above  or  below ;  the  angle  which  the  displaced  line 
thus  makes  with  the  primary  line  of  regard  is  called  "  the 
angle  of  vertical  displacement."  The  "  angle  of  lateral 
displacement"  is  formed  by  rotation  about  the  vertical 
axes. 

Torsion  of  the  Eye-ball.  —  By  combining  an  apparent 
rotation  on  the  antero-posterior  axis  with  lateral  or  vertical 
displacements  the  eye  is  brought  into  a  series  of  oblique 
positions.  Such  movement  is  called  "torsion  "  of  the  eye. 
The  angle  which  measures  the  amount  of  this  movement  is 
called  "  the  angle  of  torsion."  The  law  which  is  assumed  to 
govern  all  of  this  class  of  movements  —  namely,  combined 
movements  sideways  and  either  up  or  down  —  is  called 
"  Listing's  law."  It  has  been  stated  by  Helmholtz  as  fol- 
lows :  "  When  the  line  of  regard  passes  from  its  primary 
position  into  any  other  position,  the  torsion  of  the  eye  (as 
measured  by  the  angle  of  torsion)  in  the  second  position 
is  the  same  as  if  the  eye  were  turned  about  a  fixed  axis 
standing  perpendicular  to  both  the  first  and  the  second 
positions  of  the  line  of  regard." 

Into  the  details  involved  in  the  application  of  the  law 
that  controls  the  rotation  and  torsion  of  the  eye,  we  think 
it  unnecessary  to  enter.  One  principle  is  of  the  highest 
importance ;  it  is  illustrated  by  all  the  movements  of  the 


330 


PHYSIOLOGICAL  PSYCHOLOGY. 


eye.  The  construction  of  the  field  of  vision,  whether  monoc- 
ular or  binocular,  is  a  synthetic  mental  achievement  depend- 
ent upon  the  varying  sensations  which  result  from  the 
wandering  of  the  point  of  regard  over  the  object.  Starting 
from  its  primary  position,  the  eye  may  come  round  by  a 
variety  of  circuits  to  the  fixation  of  any  particular  point 
of  the  object.  In  the  pursuit  of  these  circuits  it  develops 
spatial  series  of  muscular  sensations  and  successively  com- 
bines them  with  other  series  of  sensations  of  light  and 
color.  Thus  the  form  of  the  field  of  vision  is  dependent 
upon  the  wandering  of  the  point  of  regard ;  and  its  con- 
struction involves  a  progressive  synthesis  of  the  mind. 
Direct  and  Indirect  Vision.  —  Let  a  sheet  of  white  paper, 


FIG.  80  (From  Hering,  after  Hemholtz).  —  With  the  eye  at  the  distance  e-e,  and  fixated 
upon  the  centre,  the  hyperbolic  lines  which  limit  the  black  and  white  surfaces  show  the 
so-called  "  right  lines  "  of  the  field  of  vision. 


PERCEPTION  BY  THE  SENSES.          331 

having  a  black  dot  in  its  centre  to  serve  as  a  point  of 
regard,  be  held  at  right  angles  to  the  line  of  vision  with 
the  eye  fixed,  in  the  primary  position,  upon  the  point 
of  regard ;  then  straight,  thin  slits  of  black  paper  upon  this 
sheet  will  appear  bent  when  lying  outside  of  the  vertical 
and  horizontal  meridians.  Or  let  the  after-images,  left  on 
these  meridians  by  light  falling  through  very  narrow 
straight  slits,  be  studied  when  torsion  of  the  eye  takes 
place,  and  these  images  will  be  found  themselves  to  suffer 
torsion.  The  amount  and  the  kind  of  torsion  suffered  by 
the  after-images  in  the  second  of  the  above-mentioned 
experiments,  may  be  discovered  by  use  of  a  rectangular 
cross.  The  image  of  such  a  figure  is  itself  distorted  as 
follows  for  the  different  torsions  of  the  eye :  Upward  and 

to  the  right,  thus,  ^"^ ;     upward  and  to  the  left,     ^^  ; 

downward  and  to  the  right,  "y*^ ;   downward  and  to  the 

/  \ 

left,  ~~r~  .     By  connecting  the  lines  in  the  field  of  vision, 

as  affected  by  all  the  possible  torsions  of  the  eyes,  the 
accompanying  figure  is  obtained  (see  Fig.  80). 

It  follows,  then,  that  only  those  objects  which  are  seen 
by  direct  vision  (that  is,  whose  images  lie  in  the  line  of 
regard  when  the  eye  is  in  its  primary  position)  appear  in 
their  actual  place ;  objects  seen  in  indirect  vision  appear 
at  the  place  which  they  would  assume  if  their  retinal 
images  were  transposed  to  the  point  of  regard  and  its  im- 
mediately surrounding  points.  The  lines  of  the  image  do 
not  correspond  to  the  lines  of  the  objective  thing ;  they  are 
constructed  by  a  .^nthesis  of  sensation-complexes  of  local 
retinal  signs  and  muscular  sensations  derived  from  the 
movement  of  the  eye. 

Sensations  from  Accommodation  of  the  Eye.  —  The  mus- 
cular sensations  —  or,  as  they  are  sometimes  called,  the 


332 


PHYSIOLOGICAL  PSYCHOLOGY. 


"  feelings  of  effort "  —  which  accompany  changes  of  the 
focus  of  the  eye  in  accommodating  for  near  distances, 
enter  into  the  data  of  visual  perception.  These  sensations 
have  not,  however,  a  very  clear  and  fixed  value.  If  we 
regard  a  black  thread,  stretched  vertically  against  a  white 
background,  with  one  eye,  through  an  aperture  in  a 
shield,  we  shall  find  that  we  can  tell  little  as  to  its  abso- 
lute distance.  Yet  we  can  discriminate  changes  in  its 

o 

distance  with  considerable  accuracy  by  changes  in  accom- 
modation. -  Helmholtz  found  that  he  required  a  stronger 
accommodation  to  see  a  red  than  a  blue  stripe,  through  a 
tube. 

Identical  and  Corresponding  Points.  —  The  theory  of  binoc- 
ular vision,  of  normal  developed  vision  with  two  eyes  in 

motion    and    acting    as    one 
organ,  introduces    other  im- 
portant   considerations.       If 
the  two  retinas  were  exactly 
similar    and    perfectly    sym- 
metrical, they   would   admit 
of  being  theoretically  super- 
imposed.     On    such   retinas,  , 
when  the  eyes  were  parallel,  I 
every  single  point  of  an  ob-l 
ject   would    have   its    image/ 
^VM-TYI^/I  ni~vrvr»  ^-"^^  "  identical " 
as,  —  upon 

points,  that  is,  whose  position 
would  be  mathematically  the  4 
same  with  reference  to  the  centre  of  each  retina. 

No  individual,  however,  has  perfectly  symmetrical  or 
similar  retinas ;  and  the  eyes  of  every  individual  are 
chiefly  active  in  other  positions  than  that  called  primary. 
Those  points  on  the  two  retinas  —  ordinarily  not  precisely 
identical  —  which  do  in  fact  act  together  are  therefore 


FIG. 


81.  -Diagram  to   illustrate    the     foi>med  UPO11  tWO 

of  both  reti 


be  seen  single. 


PEKCEPTION    BY   THE   SENSES. 


333 


called  "  corresponding."  In  other  words,  the  points  of  the 
two  retinas,  falling  upon  which  the  two  images  of  a  point 
in  the  object  are  ordinarily  seen  as  one  point,  are  corre- 
sponding. 

In  certain  cases,  moreover,  points  of  the  retina  which 
do  not  customarily  act  together  do,  as  a  matter  of  fact, 
cover  each  other ;  in  such  cases  the  two  points  are  some- 
times called  "  covering  "  points.  Indeed,  experiment  shows 
that  considerable  reciprocal  substitution  takes  place  among 
the  different  points  of  the  two  retinas.  When  the  lines  of 
regard  lie  parallel  in  the  plane  of  the  horizontal  meridian 
of  the  two  retinas,  the  vertical  meridians  do  not  correspond. 
Yet  a  vertical  meridian  of  the  left  eye,  with  its  upper  end 
inclined  to  the  left,  may  be  conjoined  with  a  vertical 
meridian  of  the  right  eye  that  has 
its  upper  end  inclined  at  about  \ 

the  same  angle  to  the  right  (see  /  \ 

Fig.  80). 

On  this  point  also,  then,  the 
true  theory  of  vision  receives 
further  confirmation.  Perception 
involves  a  fusion  or  synthesis  of 
sensation-complexes,  the  nature 
and  strength  of  which  is  deter- 
mined, not  simply  by  the  mathe- 
matical construction  of  the  eye, 
but  by  the  data  and  development 
of  conscious  experience. 

The  Double  Images.  —  If  we 
hold  a  finger  before  the  eyes  and 
look,  not  at  it,  but  at  a  distant 
wall  or  at  the  sky ;  or  if  we 

nnint  tViP   fino-pr    af    «JATYIP    rlicfonf     Been  single»  but  if  the  image  of  6 

poi  inger  at  some  distant    fall  on  the  left  eye  at  6>  an(fon  the 

object,  and  keep  our  eyes  steadily  right  eye  at  4' !t  wlu  appear  double' 
fixed  on  that  object ;  two  transparent  images  of  the  finger, 


FIG.  82.— Diagram  to  illustrate 
phenomena  of  double  vision.  If  the 
image  of  the  point  6  fall  in  one  eye 
on  6,  and  in  the  other  on  7,  the  dis- 
tance of  the  two  images  seen  will 
equal  that  between  6  and  7.  If  the 
image  of  a  fall  on  5  and  5,  it  will  be 


334 


PHYSIOLOGICAL   PSYCHOLOGY. 


instead  of  one  solid  finger,  will  be  seen.  By  experimenting 
in  this  way  one  solid  object  may  readily  be  made  to  appear 
to  pass  through  another.  If  two  objects  very  similar  —  for 
example,  the  two  corresponding  fingers  —  be  held  a  little 
way  apart,  at  a  foot  distant  and  against  a  clear  sky,  one 
solid  and  two  transparent  objects  may  be  made  to  appear, 
by  combining  the  two  middle  images  and  keeping  the  two 
outside  images  dissociated.  In  the  case  of  a  regular  small 
pattern  —  like  the  pattern  of  some  carpets,  or  wall-papers, 
or  the  spaces  of  a  wire-grating  —  the  entire  two  systems 
of  double  images  may  be  slipped  the  width  of  the  pattern 
simultaneously  to  one  side,  and  thus  combined  into  a  new 
system  of  solid  forms. 

Now  it  is  obvious  that  the  relations  of  the  two  images  of  an 

object  cannot  remain  un- 
changed when  the  eyes 
are  moved  from  their 
primary  position.  If  the 
eyes,  for  example,  are 
converged  on  any  near 
object,  only  the  images 
formed  on  the  central 
spots  of  the  two  retinas 
are  exactly  identical  and  J 
corresponding.  These 
points  alone  are  abso- 
lutely identical ;  but 
points  lying  very  near 
to  them  are  also  seen 
single  because  they  are^ 
as  it  were,  accustomed 
to  act  together.  In 
other  words,  their  local 
signs  for  both  retinas 
are  not  so  unlike  that 


FIG.  83  (from  Hering).— -/, /,  the  sash  of  the 
window,  and  p  the  black  spot  fixated.  On  the  left 
line  of  vision  I,  b  lies  a  distant  object,  and  on  the 
right  line  r,  e  another  object.  The  images  of  6  and 
e,  as  well  as  the  image  of  p,  fall  on  the  place  of 
direct  vision,  and  therefore  on  corresponding  points 
of  the  two  retinas. 


PERCEPTION  BY  THE  SENSES.          335 

they  do  not  readily  fuse.  They  have  indeed  been 
accustomed  to  fuse,  with  one  another.  All  objects,  how- 
ever, which  lie  nearer  or  more  remote  than  the  point 
fixated  by  the  eye  are  likely  to  be  seen  double ;  and  those 
which  lie  much  below  or  above,  or  to  either  side,  of  this 
point,  are  also  likely  to  be  seen  double;  that  is  to  say, 
images  of  these  objects  do  not  fall  on  corresponding  points 
of  the  two  retinas. 

Calculation  of  the  Horopter.  —  The  sum  of  all  the  points 
which  are  seen  single,  while  the  point  of  regard  remains 
the  same,  is  called  the  "  horopter."  Much  ingenuity  has 
been  displayed  in  calculation,  experiment,  and  discussion, 
to  determine  the  exact  nature  of  the  horopter.  It  has  been 
held  to  be  a  surface  (plane  or  curved),  a  circle,  a  line,  a 
number  of  connected  points.  It  cannot  be  determined  by 
calculation,  because  the  eye  in  action  is  not  a  strictly  math- 
ematical instrument.  It  cannot  be  determined  by  experi- 
ment upon  any  one  person,  under  one  set  of  circumstances, 
for  all  persons  under  varying  circumstances.  The  horopter 
is  a  psychological  affair,  and  its  actual  determination  depends 
upon  experience,  habit,  attention,  and  individual  idiosyn- 
crasies. 

With  this  understanding  of  the  matter  we  give  the  fol- 
lowing conclusions  of  Meissner  as  summaried  and,  in  most 
respects,  confirmed  by  Le  Conte^  With  the  eyes  in  the 
primary  position,  the  horopter  is  a  plane  perpendicular  to 
the  median  line  of  sight.  [On  the  contrary,  another  obser- 
ver, using  a  "  very  delicate  method  "  of  determining  whether 
we  are  seeing  double  or  not,  decides  that  "  the  horopter  is 
a  circle  where  the  fixation-point  is  median  and  nearly  in 
the  primary  plane."]  For  all  nearer  points  in  the  primary 
plane  it  is  a  line  which  dips  toward  the  observer  with  an 
inclination  to  the  visual  plane,  increasing  with  the  near- 
ness of  this  point  of  regard.  When  the  plane  of  vision 
is  turned  upward,  the  inclination  of  the  horopteric  line 


336  PHYSIOLOGICAL   PSYCHOLOGY. 

increases ;  when  it  is  turned  downward,  it  decreases  until 
it  becomes  zero  at  about  45°,  and  then  expands  into  a 
plane. 

Convergence  of  the  Axes.  —  In  fixating  the  point  of 
regard  for  vision  of  a  near  object  with  both  eyes,  the 
lines  of  vision  must  converge  upon  the  object.  In  con- 
vergence the  eyes  rotate  upon  the  axis  in  opposite  direc- 
tions. In  lowering  the  plane  of  vision,  convergence 
naturally  takes  place ;  but  in  elevating  this  plane  as  in 
looking  upon  distant  objects,  the  lines  of  regard  diverge 
toward  the  parallel  position. 

Convergence  may  be  "  symmetrical "  or  "  asymmetrical." 
In  the  former  case,  the  two  lines  of  regard  are  turned 
inward  at  equal  angles,  and  the  point  of  regard  is  kept  in 
the  median  plane  of  vision;  in  the  latter,  the  point  of 
regard  is  outside  of  the  median  plane,  and  the  two  eyes 
are  either  turned  at  unequal  angles  inward,  or  else  one  is 
turned  inward,  and  the  other  outward  at  a  smaller  angle. 

Changes  of  accommodation  naturally  accompany  changes 
in  convergence  of  .the  eyes ;  and  the  resulting  sets  of  sen- 
sation-complexes enter  into  the  perceptive  construction  of 
space-form  given  to  the  object. 

Influence  of  Effort  in  Vision.  —  A  direction  of  attention 
and  an  effort  to  see  are  probably  implied  in  convergence 
of  the  eyes.  The  eyes  of  new-born  children,  and  eyes  that 
are  recently  couched,  as  a  rule,  move  in  parallel  lines. 
Arrest  of  attention  brings  the  two  eyes  into  use  as  one 
organ.  In  this  way  the  sensations  which  arise  when  the 
muscles  are  innervated  so  as  to  produce  convergence  are  of 
marked  importance  in  the  construction  of  the  most  elab- 
orate and  intelligent  visual  perceptions. 

It  is  held  by  some  authorities  that  the  innervation  of 
both  eyes  is  equal  even  when  the  movements  of  the  two  are 
unequal ;  for  each  eye  is  then  under  the  influence  of  two 
innervations,  one  of  which  is  directed  toward  turning  both 


PERCEPTION  BY  THE  SENSES.  337 

eyes  right  or  left,  and  the  other  toward  turning  them 
inward  or  outward.  In  one  eye  the  two  innervations 
would  support,  and  in  the  other  eye  they  would  oppose 
each  other.  As  a  result  they  compensate  each  other ;  and 
the  will  may  be  regarded  as  guiding  its  pair  of  horses  by  a 
pull  upon  one  rein.  However  this  may  be,  there  can  be 
no  doubt  that  the  mental  representatives  of  the  different 
motions  and  positions  are  important  factors  in  that  mental 
construction,  called  the  "  field  of  sight." 

Conditions  of  Stereoscopic  Vision.  —  By  the  various  "helps" 

already  described  stereoscopic  vision  is  made  possible. 
Without  the  joint  activity  of  both  eyes,  it  is  probable  that 
such  vision  cannot  take  place.  If  this  be  true,  the  field  of 
monocular  vision  could  be  directly  apprehended  only  as  a 
plane ;  since  all  immediate  perception  of  depth  would 
depend  upon  the  existence,  and  the  coupling  and  uncoup- 
ling of  the  double  images,  together  with  the  related  changes 
in  muscular  and  tactual  sensations  as  the  two  eyes  move 
upon  their  axes.  It  is  certain  that  our  immediate  percep- 
tion of  the  depth  of  objects  with  one  eye,  if  such  perception 
exist  at  all,  is  exceedingly  inadequate. 

It  is  undoubtedly  true  that,  in  adult  vision,  we  do  per- 
ceive objects  to  a  certain  extent  stereoscopically  with  one 
eye  closed.  But  it  is  probable  that  such  perception  is 
mediate  and  indirect ;  that  is,  it  is  accomplished  solely  by 
secondary  means  of  vision.  Among  such  means  are  the 
varying  intensities  of  light  and  color,  changes  in  apparent 
magnitude,  etc.,  —  all  resting  on  the  basis  of  associations 
long  ago  made  by  using  the  two  eyes  and  the  hands.  By 
simple  experiments  with  one's  self  one  may  be  convinced 
how  easy  it  is,  when  seeing  with  only  one  eye,  to  reduce  all 
vision  to  indistinct  patches  of  light  and  color  on  a  visual 
plane. 

There  is  no  doubt  that  the  double  images  which  result 
from  the  use  of  the  eye  in  motion  afford  data  for  the  per- 


338  PHYSIOLOGICAL   PSYCHOLOGY. 

ception  of  the  solidity  of  objects.  It  is  more  difficult  to  say 
just  how  this  service  is  rendered.  Artificial  stereoscopic 
vision  has  made  every  one  familiar  with  the  fact  that  the 
two  images  of  every  object  differ  as  furnished  by  the  two 
eyes.  The  right  eye  sees  the  object  farther  around  on  its 
right  side,  the  left  on  its  left.  Every  minute  portion  of  a 
solid  object,  provided  such  portion  lies  a  little  way  out  of 
the  line  of  regard,  instead  of  consisting  of  two  exactly 
similar  sets  of  lines  that  might  be  exactly  superimposed, 
consists  of  two  sets  of  minute  curves  that  are  partial 
images  of  its  lines  and  are  different  for  each  eye.  In  some 
manner  the  perception  of  solidity  is  substantially  aided 
by  the  fusion  of  these  partial  images. 

Furthermore,  in  all  ordinary  stereoscopic  vision  the 
motion  of  the  eyes  successively  unites  and  separates  the 
double  images  of  the  objects  seen.  In  viewing  all  objects 
of  any  size  we  may  by  attention  become  aware  of  the  fact 
that  we  are  sweeping  over  the  field  of  vision  with  a  moving 
point  of  regard.  Even  in  the  apparently  instantaneous 
perception  of  a  more  minute  object,  the  eyes  are  actually 
engaged  in  making  short  and  rapid  excursions  around  the 
primary  point  of  regard.  It  has  thus  been  found  possible 
to  claim,  with  much  plausibility,  that  the  localization  of 
stereoscopic  figures  corresponds  exactly  with  the  kind  and 
degree  of  motion  necessary  to  produce  fusion  of  the  double 
images. 

On  the  other  hand,  that  movement  of  the  eyes  is  not 
necessary  to  stereoscopic  vision  for  trained  adult  eyes,  is 
proved  by  what  is  known  as  "Dove's  experiment."  A 
field  of  vision,  composed  of  two  stereoscopic  pictures,  can 
be  constructed  when  lighted  by  an  electric  spark;  the 
•^thnj-  sec.  which  the  flash  of  the  spark  occupies  is  far  too 
brief  a  time  to  admit  of  convergence  or  of  change  in  the 
point  of  regard.  But  we  probably  have  in  this  experience 
one  of  those  many  cases  where  a  complex  product  of  per- 


PERCEPTION  BY  THE  SENSES.          339 

ception  results  from  the  fact  that  the  sensation-complexes 
primarily  aroused  by  the  stimulus  call  into  consciousness, 
as  fused  with  them,  a  variety  of  images  of  other  secondary 
sensation-complexes.  In  other  words,  instantaneous  binocu- 
lar vision  of  solidity  and  depth  of  objects,  like  monocular 
vision  of  solidity  and  depth  in  general,  is  secondary  and 
^dependent  upon  previous  experience  with  both  eyes  in  motion. 
Localizing  of  the  Third  Dimension,  —  Perception  of  the 
depth  and  distance  of  objects  depends  primarily,  therefore, 
upon  vision  with  two  moving  eyes.  For  such  perception 
Hering  has  proposed  the  following  law :  All  the  lines  or 
points  whose  images  lie,  with  a  given  position  of  the  point 
of  regard,  in  the  vertical  horopter,  appear  clearly  defined 
on  a  surface  which  is  either  plane  or  slightly  cylindrical ; 
and  all  the  lines  or  points  lying  this  side  of  the  vertical 
horopter  and  whose  images  have  a  "  crossed  disparateness  " 
(that  is,  the  left  one  of  the  double  images  belongs  to  the 
right  eye,  and  the  right  image  to  the  left  eye)  appear  in 
front  of  this  surface ;  while  those  lying  beyond  the  horop- 
ter and  whose  images  have  an  "  uncrossed  disparateness  " 
(that  is,  the  right  image  belongs  to  the  right  eye,  and  the 
left  image  to  the  left  eye)  appear  behind  the  surface  on 
which  whatever  lies  in  the  horopter  is  seen. 

Of  course,  every  law  like  the  foregoing  must  be  trans- 
lated into  terms  of  psychical  representation  in  order  to 
be  a  real  law  of  perception.  It  implies  the  truth  of  the 
general  theory,  that  interpretation  of  the  images  for  the 
discernment  of  distance  with  motionless  eyes  is  an  acquired 
art,  which  is  dependent  upon  previous  combination  of  the 
retinal  signs  of  both  eyes  with  muscular  sensations  arising 
from  the  innervation  and  movement  of  the  eyes. 

The  "  old  psychology  "  was  accustomed  to  hold  that  we 
cannot  perceive  the  third  dimension  —  the  depth  and  dis- 
tance of  objects  —  with  the  eyes.  Such  perception,  it 
held,  always  results  from  muscular  sensations  of  the  entire 


340  PHYSIOLOGICAL  PSYCHOLOGY. 

body,  or  of  the  gross  members  of  the  body,  which  have 
become  associated  with  visual  sensations.  In  other  words, 
a  translation  from  sight  into  touch  and  muscular  move- 
ment was  thought  to  be  necessary  in  order  to  see  the  depth 
and  distance  of  objects.  This  view  is  undoubtedly  erro- 
neous. Depth  and  distance  are  immediately  perceived  by 
sight;  but  such  perception  comes,  primarily,  only  through 
that  developed  vision  which  uses  both  eyes  in  motion,  — 
changing  the  convergence  of  the  axes  and  coupling  and 
uncoupling  the  double  images  with  a  varying  point  of 
regard. 

VISUAL  JUDGMENT  AND  ERRORS  OF   VISUAL  PERCEPTION. 

Most  of  our  experience  in  stereoscopic  vision  and  vision 
of  perspective  of  remote  objects  avails  itself,  as  it  were,  of 
other  helps  that  are  not  indispensable,  absolutely,  to  the 
construction  of  a  field  of  vision.  These  are  sometimes  called 
"secondary"  Vision  by  their  aid  is  often  called  "judg- 
ment," in  distinction  from  so-called  immediate  perception. 
But  judgment,  in  the  sense  of  discerning  and  relating 
activity  of  mind,  is  involved  in  all  perception.  The  only 
place  where  we  can,  apparently,  fix  any  line  of  distinction 
lies  between  those  data  of  sensation  which  are  necessary 
to  any  normal  binocular  vision  whatever,  and  those  less 
primary  means  of  assistance  in  seeing  (or  judging)  the 
relative  positions  and  distances  of  remoter  objects  that 
depend  upon  changing  aspects  of  these  objects.  The  need 
of  so-called  "  secondary  helps  "  is  the  greater  because,  at 
distances  farther  than  from  twenty  to  forty  feet,  the  changes 
which  accompany  convergence  and  accommodation  become 
practically  inappreciable. 

Five  or  more  classes  of  secondary  helps  for  stereoscopic 
vision,  and  vision  of  perspective  for  distant  objects,  may 
be  enumerated.  Among  them  the  following  are  the  more 
important. 


PERCEPTION  BY  THE  SENSES. 


341 


Course  of  the  Limiting  Lines.  —  The  lines  which  limit  any 
object,  when  they  are  constructed  by  the  moving  eye,  de- 
termine our  perception  of  the  distance  and  form,  in  depth, 
of  that  object.  If  these  lines  become  confused,  or  run  in 
directions  strongly  to  contradict  previous  experience,  we 
are  liable  to  errors  in  perception.  Especially  when  the 
bottom  lines  of  a  distant  object  are  covered,  its  distance 
and  shape  in  the  third  dimension  become  uncertain.  The 
same  arrangement  of  lines,  when  it  admits  of  two  inter- 
pretations, can  be 
perceived  in  either 
one  of  two  ways ;  for 
example,  (as  in  the 
case  of  Fig.  84,)  as 
either  a  staircase  or 
a  portion  of  an  over- 
hanging wall.  In- 


deed, in 
such  an 
rhythmic 


viewing 

object    a 

change 


FIG.  84   (from  Wundt).  — a  can  be  made  to  appear 
either  nearer  or  farther  off  than  6. 


from  one  form  of  perception  to  the  other  may  occur  as  a 
result  of  a  rhythmic  change  in  the  fixation  of  attention 
and  in  accommodation  (see  also  Fig.  85). 

On  the  other  hand,  the  charac- 
ter of  the  limiting  lines  may  be 
such  as  to  forbid  more  than  one 
way  of  perceiving  the  object. 

Mathematical  Perspective.  —  The 
size  of  the  angle  of  vision  which  is 
covered  by  the  object,  whether 
near  or  remote,  is  another  of  the 
so-called  secondary  helps.  In  this 
way  objects  of  known  size  are  seen 
as  placed  at  a  distance  necessary 
to  give  them  their  apparent  size.  The  street  appears  nar 


Fio.  85.— Fire!  one,  then  the 
other  corner  of  the  figure  may  be 
drawn  forward,  partly  at  will. 


342  PHYSIOLOGICAL   PSYCHOLOGY. 

rower  and  more  distant,  the  houses  lower  and  more  remote, 
in  the  upper  part  of  its  visual  picture.  The  tracks  of  a 
railroad  appear  to  converge  in  the  distance ;  and  the  same 
thing  is  true  of  the  sides  of  the  table  or  box  near  which 
we  are  standing. 

Aerial  Perspective,  —  More  distant  objects,  on  account  of 
the  amount  of  atmosphere  through  which  the  rays  of  light 
reflected  from  them  have  to  pass,  are  more  dim  in  outline 
and  of  a  changed  shade  of  color.  These  alterations  in  the 
character  of  the  image  furnish  another  secondary  help  in 
our  vision  of  perspective.  Accordingly,  things  are  seen 
nearer  in  an  atmosphere  clearer  than  ordinary,  more  dis- 
tant in  one  less  clear. 

Size  and  Direction  of  the  Shadows. — In  the  morning  or 
evening  light,  when  all  shadows  are  lengthened,  the  dis- 
tance of  objects  is  also  lengthened.  The  arrangement  of 
the  lights  and  shadows  is  by  far  the  most  important  datum 
for  perceiving  the  character  of  objects  like  intaglios  or 
medallions.  A  change  in  this  arrangement,  so  as  to  sub- 
stitute light  and  shadow  for  each  other  throughout,  con- 
verts an  intaglio  into  a  medallion,  and  vice  versa. 

Number,  Duration,  and  Intensity  of  the  Spatial  Series, — 
When  the  eye  is  in  motion,  as  in  vision  of  all  objects  not 
very  minute  and  very  near,  the  number,  duration,  and 
intensity  of  the  different  spatial  series  of  sensation-com- 
plexes called  forth  by  the  motion  are  of  influence  in  deter- 
mining the  outline-form,  size,  and  distance  of  objects.  The 
greater  the  number  of  the  successive  sensation-complexes  it 
produces,  the  greater  our  estimate  of  the  size  of  the  object. 
For  this  reason  the  same  extension  of  a  line  or  surface, 
when  broken  up  into  parts  by  intersecting  lines,  seems 
larger  than  when  perceived  as  an  uninterrupted  whole» 
This  principle  is  made  use  of  in  repetitions  of  figures  upon 
walls,  columns,  etc.,  in  architecture. 

The  intensity  of  the  sensation-complexes  entering  into  a 


PERCEPTION  BY  THE  SENSES.          343 

spatial  series  has  also  an  influence  on  our  estimate  of  the 
size  of  the  object  perceived.  The  size  of  the  object  is 
increased  by  viewing  it  with  moving  eyes  when  the  muscles 
are  lamed  or  tired.  In  paralysis  of  a  muscle  of  »the  eye 
(for  example,  the  rectus  externus),  objects  seen  by  the  eye 
moving  in  its  shortened  circuit  are  located  where  they 
would  have  been  if  the  same  intensity  of  muscular  sensa- 
tion had  been  necessary  to  bring  them  to  this  position  with 
a  normal  action  of  the  muscle.  On  this  principle  the  size 
of  parti-colored  and  mottled  objects  is  increased.  But  the 
absence  of  a  standard  of  judgment  may  have  the  same 
effect  on  the  repetition  of  the  standard  ;  thus  both  unusual 
monotony  and  great  variety  may  have  the  same  effect  in 
magnifying  the  size  of  the  perceived  object. 

The  duration  of  time  of  the  eye's  activity  in  perception 
also  has  a  marked  influence  on  our  estimate  of  the  size  of 
the  object.  The  length  of  time  occupied  in  mastering  com- 
plex objects  may  be  interpreted  —  especially  if  the  atten- 
tion required  is  somewhat  strict  and  painful  —  as  extensive 
magnitude. 

Influence  of  Memory  and  Will  upon  Visual  Perception.  — In 
all  adult  vision  the  mind  takes  its  token,  as  it  were,  from 
a  very  incomplete  outline  sketch  of  the  object  and  "makes 
up,"  of  itself,  the  complete  object,  by  drawing  upon  its 
store  of  memory-images.  Visual  perception  is,  therefore, 
not  simply  according  to  the  objective  character  of  so-called 
"  things "  to  be  seen ;  it  is  also  very  largely  according  to 
the  mind's  custom  in  perception.  Accordingly,  when  the 
mind's  habit  is  broken  up  for  a  time,  its  interpretation  of 
the  sensation-complexes,  and  its  synthesis  of  them  into 
recognized  objects  of  sense,  may  be  much  altered.  For 
example,  the  effect  of  the  "  pseudoscope," — an  optical 
instrument  which  by  exchanging  the  two  stereoscopic  pic- 
tures converts  convex  into  concave,  and  vice  versa, — when 
applied  to  a  complex  object,  like  a  landscape,  is  very  bewil- 


344  PHYSIOLOGICAL  PSYCHOLOGY. 

dering.  The  same  thing  is  also  true  of  the  "telestereo- 
scope,"  —  an  optical  instrument  which  enables  us  to  see  a 
larger  portion  of  a  distant  object  than  is  possible  with  two 
ordinary  eyes,  somewhat  after  the  fashion  of  a  pair  of  opti- 
cal organs  in  the  sides  of  a  gigantic  head. 

Within  certain  limits  we  can  see  what  we  choose  to  see. 
It  is  held  by  many  excellent  observers  that,  without  any 
change  of  focus  or  of  convergence,  we  can  render  any 
object  in  the  field  of  vision  clearer  by  directing  attention 
upon  it.  Even  when  the  object  lies  far  to  one  side  of  the 
field,  this  effect  —  though  difficult  to  produce  —  may  be 
attained  by  trained  observers.  In  the  case  of  perception 
with  a  moving  eye  we  can,  to  a  certain  extent,  decide  the 
area  over  which  the  point  of  regard  shall  sweep  and  the 
relative  attention  to  be  given  to  the  subdivisions  of  this 
area.  Furthermore,  and  especially  in  the  case  of  geomet- 
rical figures,  it  often  lies  in  our  power  to  decide  how  we 
will  interpret  certain  data  which  admit  of  more  than  one 
interpretation. 

Accuracy  of  Visual  Perceptions,  —  Our  estimate  of  the 
length  of  visual  lines  and  of  the  size  of  visual  surfaces  is 
relative,  not  absolute ;  it  falls,  therefore,  to  some  extent, 
under  the  principles  discussed  in  Weber's  law.  The  fine- 
ness of  ocular  judgment  is  greater  for  horizontal  than  for 
vertical  distances.  It  is  much  less  accurate  when  the  dis- 
tances compared  lie  in  different  directions.  In  particular, 
points  lying  at  a  vertical  distance  of  20  mm.  are  estimated 
as  equally  far  away  with  those  lying  at  a  horizontal  dis- 
tance of  25  mm.  Estimates  of  direction  and  distance  are , 
much  more  inaccurate  when  made  with  only  one  eye. 

The  principal  data  which  enter  into  visual  judgments  of 
length,  etc.,  are  probably  the  local  signs  of  the  retina  as 
associated  with  memory-images  of  sensations  of  motion, 
and  minute  changes  of  the  coloring  of  muscular  sensations 
ao  directly  dependent  upon  movement  in  accommodation 


PEKCEPTION  BY  THE  SENSES.          345 

and  convergence.  Helmholtz  found  that  a  displacement  of 
the  middle  one  of  three  nails,  when  set  in  an  otherwise 
straight  line,  corresponding  to  a  variation  of  only  0.0044  mm. 
in  the  position  of  the  retinal  image,  could  be  detected. 
And  Weber  showed  that  a  distinct  muscular  sensation  is 
attached  to  a  displacement  of  the  most  sensitive  spot  of 
the  retina  of  not  more  than  -^T  of  a  Parisian  line. 

More  Complex  Estimates  of  Visual  Magnitudes.  —  The  real 
and  the  apparent  magnitude  of  an  object  are,  of  course,  so 
related  that  one  is  dependent  upon  the  other.  By  the 
"  apparent  magnitude  "  of  an  object  we  mean  its  size  as 
perceived  (or  judged)  by  the  magnitude  of  the  angle  cov- 
ered by  its  image,  or  by  the  extent  of  the  external  surface 
simultaneously  excited  by  the  rays  of  light  reflected  from 
the  object.  The  "  real  magnitude  "  is  its  size  as  definitely 
measured  by  certain  fixed  standards  of  measurement  formed 
on  the  basis  of  generalizations  from  the  use  of  both  eye  and 
hand. 

Distance,  apparent  magnitude,  and  real  magnitude  may 
therefore  be  connected  as  three  factors  of  one  problem  pro- 
posed to  the  perceptive  power  of  the  eye.  Given  both  the 
apparent  and  the  real  magnitude  of  an  object,-and  we  judge 
of  its  distance  according  to  our  experience  of  how  large 
an  object  of  the  known  size  ought  to  look  at  an  assumed 
distance.  The  distance  at  which  the  object  is  perceived 
may  be  said  to  be  an  hypothesis  framed  to  reconcile  the 
known  with  the  apparent  magnitude.  Distance  and  appar- 
ent magnitude  being  given,  real  magnitude  is  judged  as 
that  which  the  object  would  need  to  have  in  order  to  appear 
so  large  as  it  does  appear  at  the  known  distance.  When 
either  of  the  two  necessary  data  is  lacking  or  obscured  we 
fall  back,  as  it  were,  upon  such  secondary  helps  as  aerial 
perspective,  etc. 

Perception  of  Motion  by  the  Eye.  —  The  data  and  processes 
already  described  furnish  the  explanation  of  our  percep- 


346  PHYSIOLOGICAL  PSYCHOLOGY. 

tions  of  the  direction,  speed,  and  extent  of  the  motion  of 
objects,  by  the  eye.  Here,  as  elsewhere,  we  seem  to  require 
a  distinction  between  such  perceptions  as  are  most  primary, 
and  involve  the  fusion  of  the  local  signs  into  those  spatial 
series  which  make  it  impossible  for  consciousness  to  disen- 
tangle the  component  factors,  and  those  secondary  percep- 
tions where  judgment  is  consciously  exercised  in  estimating 
the  value  of  various  more  or  less  separable  data.  The 
latter  form  of  perception  is  more  correctly  described  as 
an  "  inference  "  to  the  motion  of  a  body  from  seeing  it  at 
different  places  in  space  at  successive  intervals  ;  the  former 
appears  rather  as  elementary  and  immediate  perception  of 
motion  on  the  basis  of  just  perceptible  changes  in  the 
requisite  sensation-complexes.  We  may  have  a  perception 
of  motion  when  the  interval  between  the  two  appearances 
of  the  moving  body  is  too  minute  to  be  observed.  For 
example,  two  impressions  0.045  sec.  apart  can  barely  be  dis- 
tinguished as  two;  but  the  direction  of  the  motion  of  a 
light  can  be  perceived  when  the  difference  between  the 
beginning  and  the  end  of  the  motion  is  only  0.014  sec. 
On  the  lateral  portions  of  the  retina  two  disks,  so  near  as 
not  to  be  seen  as  two,  can  easily  be  seen  to  change  place 
on  the  slightest  movement. 

In  general,  our  judgments  in  perception  of  motion  by 
the  eye  imply  the  existence  of  some  point  which  may  be 
regarded  as  fixed,  and  the  application  of  a  standard  of 
measurement.  If  no  one  object  in  the  field  of  vision  is 
recognized  as  stationary,  such  perception  becomes  exceed- 
ingly vague,  and  the  perceptible  mininum  of  motion 
becomes  about  ten  times  as  great.  When  the  organ  is 
in  the  primary  position,  the  point  of  regard  furnishes  the 
means  for  placing  things  in  right  relations  to  ourselves  and 
to  each  other. 

Perception  of  motion  may  then  arise  in  one  of  two  ways. 
The  object  may  change  its  relative  position  in  the  field  of 


PERCEPTION  BY  THE   SENSES.  347 

vision ;  this  involves  the  successive  stimulation  of  contig- 
uous areas  of  the  retina  with  images  that  are  sufficiently 
alike  to  be  regarded  as  one  real  object.  But  perception  of 
motion  may  also  be  produced  by  the  successive  stimulation 
of  the  same  area  of  the  retina  with  images  that  are  too 
dissimilar  to  be  regarded  as  one  object. 

In  perceiving  all  movements  of  much  extent,  however, 
the  eyes  follow  the  object.  When  both  eyes  move  in  such 
a  way  that  the  point  of  regard  remains  fixed  on  the  object, 
our  perceptions  of  the  direction  and  amount  of  motion  are 
dependent  upon  changes  in  the  muscular  and  tactual  sen- 
sations evoked  by  the  eye's  changes  of  position.  That  is 
to  say,  we  judge  the  movement  of  the  object  on  a  basis  of 
judgment  as  to  the  positions  and  movement  of  the  eyes 
themselves.  But  we  may  need  to  turn  the  head,  or  even 
the  body,  in  order  to  follow  with  the  eye  the  moving 
object.  In  this  case  the  sensation-complexes  originating  in 
the  action  of  the  muscles  and  skin  of  the  head  and  neck, 
etc.,  furnish  indispensable  data  which  enter  into  our  com- 
putation. These  data  must  have  such  an  established  value 
in  consciousness  as  to  indicate  the  successive  positions  of 
the  moving  parts  of  the  body,  or  else  we  cannot  "  see  " 
(perceive  or  judge)  how  far,  and  in  what  direction,  the 
object  has  moved. 

Perception  of  objects  in  motion  implies  perception  of 
objects  at  rest.  Objects  are  perceived  at  rest,  either  when, 
our  organs  of  vision  being  themselves  at  rest,  the  images 
of  the  objects  do  not  change  their  position  in  the  field  of 
vision,  or  when  the  sensations  of  motion  occasioned  by 
moving  the  organs  are  such  as  we  know  by  experience 
correspond  to  those  changes  in  the  position  of  the  images 
which  are  occasioned  by  objects  actually  remaining  at  rest. 

Thus  what  is  really  moving,  and  what  is  really  at  rest, 
in  a  complex  field  of  vision,  often  becomes  a  very  compli- 
cated and  difficult  problem  for  the  mind  to  solve  on  data 


348  PHYSIOLOGICAL   PSYCHOLOGY. 

furnished  by  the  eye  alone.  Few  things  connected  with 
the  general  subject  are  more  impressive  than  the  errors  of 
visual  perception  which  originate  under  unfavorable  cir- 
cumstances. Indeed,  where  we  do  habitually  solve  the 
problem  successfully,  the  data  on  which  we  solve  it  are 
apt  to  be  overlooked.  They  are  always  very  difficult  of 
disentanglement.  Few  people  have  noticed  that,  in  every 
case  of  the  hundreds  daily  occurring,  when  we  change  the 
point  of  regard  from  a  very  remote  to  a  very  near  object, 
the  two  fields  of  view  belonging  to  the  two  eyes  rotate  in 
opposite  directions,  while  the  middle  visual  line  maintains 
its  position  in  the  median  plane. 

After-images  of  Motion,  —  Those  sensation-complexes 
which  the  mind  builds  into  perceptions  of  motion,  like 
other  sense-impressions,  leave  an  after-image.  In  this  way 
very  confusing  results  are  frequently  obtained.  For  ex- 
ample, if  a  rotating  disk,  with  a  spiral  drawn  upon  it,  be 
suddenly  stopped  rotating,  the  points  previously  seen  to 
move  toward  the  centre  are  now  seen  to  move  in  the  oppo- 
site direction.  If  one  eye  view  a  rotating  disk  directly,  and 
the  other  through  a  reversion  prism,  the  two  impressions 
result  in  confused  perception ;  but  if  the  disk  be  looked  at 
with  one  eye  until  fatigue  occurs,  and  then  that  eye  closed, 
and  a  white  surface  looked  at  with  the  other  eye,  an  after- 
image of  the  disk  rotating  in  the  opposite  direction  will 
appear. 

General  View  of  So-called  "  Errors  of  Sense."  —  The  right 
to  use  the  term  "  errors  of  sense,"  has  sometimes  been  dis- 
puted, on  the  ground  that  sense  cannot  err,  and  that  all 
error  is  really  of  the  judgment.  But  this  attempt  at  dis- 
tinction is  based  upon  a  complete  misunderstanding  of  the 
nature  of  perception.  All  perception  involves  discrimina- 
tion and  judgment ;  but  errors  in  this  sphere  are  not  by 
any  means  confined  to  the  making  of  distinctions  which 
can  be  corrected  at  will  by  revision  of  the  data,  as  it  were. 


PERCEPTION  BY  THE  SENSES.          349 

When  one  sees  a  square  of  white  paper  green  because  it 
is  on  a  red  ground,  or  yellow  because  it  is  on  a  blue 
ground,  it  is  certainly  correct  to  say  that  the  senses  are  in 
error.  The  remark  of  Lotze  is  not  unjustifiable  when  he 
affirms :  "  The  whole  of  our  apprehension  of  the  world  by 
the  senses  is  one  great  and  prolonged  deception." 

We  should  prefer,  however,  to  call  attention  to  such 
facts  as  the  following :  Clear  vision  is  always  mental  inter- 
pretation. Objects  of  sense  are  in  no  case  exact  copies  of 
ready-made  things.  The  data,  or  motifs,  and  the  laws  of 
the  mind's  constructive  and  synthetic  activity,  are  pre- 
cisely the  same  when  errors  of  sense  are  committed  as 
when  so-called  true  and  exact  perception  takes  place. 
Errors  of  sense  differ  from  hallucinations,  because  the 
former  result  from  the  activity  of  an  organism  which  is 
normal  in  structure  and  function,  while  the  latter  do  not. 

The  errors  of  visual  perception  are  almost  innumerable ; 
they  can  be  only  partially  classified,  according  as  they  fall 
under  some  one  of  the  foregoing  principles  rather  than 
others.  Certain  of  the  more  important  classes  are  the  fol- 
lowing :  — 

Errors  Due  to  the  Relations  of  the  Double  Images.  —  We 
have  already  seen  that  near  objects  erroneously  appear 
double  when  the  eye  is  adjusted  for  distant  objects,  and 
distant  objects  appear  double  when  the  eye  is  adjusted 
for  near  distances.  Solid  objects  are  sometimes  seen 
through  other  solid  objects ;  one  object  sometimes  appears 
two,  and  two  objects  appear  one ;  —  and  all  according  to 
the  law  of  the  correspondence  or  non-correspondence  of 
the  two  retinal  images. 

A  very  old  psychological  puzzle  is  proposed  in  the  ques- 
tion, Why  is  vision  single,  when  performed  with  two  eyes  ? 
The  question  implies  a  complete  misunderstanding  of  the 
whole  theory  of  visual  perception.  We  do  not  see  the 
images  at  all ;  but  —  as  we  have  learned  from  the  facts  of 


350 


PHYSIOLOGICAL  PSYCHOLOGY. 


stereoscopic  vision  —  a  chief  condition  of  the  single  vision 
of  all  solid  objects  is  that  they  shall  be  seen  with  two  eyes. 
The  fusion  of  the  data  belonging  to  the  formation  of  the 
two  images  is  the  psychical  condition  of  the  perception  of 
one  solid  object. 

Errors  of  Mathematical  Perspective.  —  A  large  class  of 
visual  errors  fall  under  laws  which  regulate  the  smallest 
observable  differences  in  the  muscular  sensations  as  related 


FIG.  86. 


FIG.  87. 


to  the  clear  perception  of  the  lines,  angles,  and  surfaces  of 
the  object  perceived.  The  fact  that  vertical  distances  are 
regularly  perceived  as  larger  than  equally  large  horizontal 
differences  has  already  been  mentioned.  On  trying  to  draw 
a  cross  with  limbs  of  equal  length 
one  is  apt  to  get  the  vertical  dimen- 
sions too  small ;  exact  squares  appeal- 
higher  than  their  breadth.  When 
comparing  magnitudes  in  the  upper 
part  of  the  field  of  vision  with  those  in  its  lower  part, 
one  is  likely  to  overestimate  the  former.  The  upper  and 
lower  half  of  an  "  S  "  or  a  figure  "  8 "  appear  of  nearly 


the  same  size  ;  but  when  they  are  inverted  ("  g "  and 
"  g "),  the  difference  in  the  size  of  the  two  halves  is 
exaggerated. 


PERCEPTION  BY   THE   SENSES. 


351 


a\ 


Errors  arising  from  the  Number  and  Variety  of  Impressions. 
—  We  are  frequently  deceived  in  a  remarkable  way  by  the 
manner  in  which  the  field  of  vision  is  filled  up.  Such 
errors  fall  in  part  under  the  principles  of  mathematical 
perspective,  but  also  in 
part  under  the  principle 
which  converts  into  "  ex- 
tensity  "  the  number  and 
intensity  of  our  sense- 
impressions. 

If  the  horizontal  dis- 
tance between  two  points 
be  exactly  half  filled  with 


FIG.  90. 


a  line,  this  line  will  ap- 
pear to  some  observers  longer  than  the  remaining  empty 
space.     A  square  intersected  by  parallel  horizontal  lines 


appears  elongated  upward,  but  one  intersected  by  parallel 
vertical  lines  appears  elongated  sideways.     If  one  of  two 


FIG. 92. 


352 


PHYSIOLOGICAL   PSYCHOLOGY. 


right  angles,  formed  by  a  line  drawn  perpendicular  to  a  hori- 
zontal line,  be  filled  with  several  lines  diverging  from  the 


FIG.  93. 

point  of  the  angle,  it  will  appear  larger  than  the  other 
right  angle,  and  the  perpendicular  will  seem  bent.     Many 

surprising  visual  errors 
result  from  combina- 
tions of  this  and  the 
foregoing  principles. 

Errors  of  Imagination 
under  the  Law  of  Habit. 
—  If  the  visual  data 
will  at  all  permit  it,  we 
incline  to  perceive  any 
visible  object  as  we 
know  that  similar  ob- 
jects are  usually  per- 
ceived. In  other  words, 
FlG- 94-  the  synthesis  of  the  vari- 

ous sensation-complexes  with  one  another,  and  with  the  re- 


PERCEPTION  BY  THE  SENSES.  353 

vived  and  associated  memory-images,  falls  under  the  law  of 
habit.  This  principle  is  constantly  taken  into  account  by 
the  pleasant  illusions  of  art.  Their  success  in  —  as  we 
say  — "  deceiving "  us  is  not  strange ;  for  this  success 
rests  upon  the  same  basis  as  all  the  normal  and  habitual 
perceptive  activity  of  the  mind. 

Many  errors  in  our  perception  of  motion  by  the  eye  are 
to  be  explained  on  the  foregoing  principle.  It  makes  no 
difference  with  the  result  whether  the  data  for  such  per- 
ceptions are  furnished  by  actual  changes  in  the  position 
of  external  things,  or  by  changes  confined  within  the 
organs  of  sense.  We  incline,  for  example,  where  two 
objects  are  seen  to  be  changing  their  relative  position,  to 
perceive  the  smaller  of  them  as  in  motion ;  we  also  over- 
estimate the  speed  of  small  bodies  in  motion,  and  under- 
estimate that  of  large  bodies. 

Errors  chiefly  Due  to  Inter-cerebral  Changes.  —  The  attempt 
to  discover  a  physiological  explanation  for  such  errors  as 
belong  to  the  class  last-mentioned  brings  us,  of  course,  to 
the  cerebral  visual  areas  as  their  primary  source.  We  have 
already  seen  that  the  phenomena  of  the  contrast  of  colors 
(p.  264  f .)  must  depend  upon  certain  inexplicable  activities 
of  the  central  organs.  The  same  thing  is  true  of  those  errors 
of  sense  which  occur  in  connection  with  the  strife  and 
prevalence  of  contours,  and  with  the  binocular  mixing  and 
contrast  of  colors. 

If  a  well-defined  image  of  some  colored  contour  be 
formed  on  one  retina,  and  on  the  corresponding  area  of  the 
other  the  image  of  a  uniformly  colored  background,  only 
the  former  will  be  visible.  This  is  called  the  "  prevalence 
of  contours."  But  if  the  contours  of  the  two  images  of 
differently  colored  objects  cross  on  the  retinas,  then  some- 
times one  and  sometimes  the  other  of  the  two  colors  will 
be  perceived  at  the  place  of  crossing.  This  is  called  "  the 
strife  of  contours."  If  four  squares  of  paper,  —  otherwise 


354  PHYSIOLOGICAL  PSYCHOLOGY. 

exactly  similar,  —  two  of  red  paper  and  two  of  blue,  have 
their  images  combined,  the  middle  one  of  the  binocular 
images  will  be  sometimes  redder,  and  sometimes  bluer, 
than  either  of  the  side-images;  but  in  no  case  will  it 
exactly  resemble  either  of  them.  This  is  called  the  "  binoc- 
ular mixing  of  colors."  If  a  white  stripe  be  placed  upon 
a  black  surface  and  divided  into  two  images,  the  right  one 
of  which  is  formed  by  looking  at  one  half  through  blue 
glass,  and  the  left  by  looking  through  gray  glass,  then  the 
right  image  will  be  seen  blue,  but  the  left  will  be  seen 
yellow.  This  is  called  "  binocular  contrast  of  colors." 

Now  in  all  these  and  similar  cases  of  deception  it  is 
plain  that  the  physiological  conditions  of  the  mixing  and 
contrast  of  the  contours  or  colors  depend  upon  combined 
and  contrasted  changes  of  the  brain  rather  than  of  the  ex- 
ternal organs  of  sense.  None  the  less,  but  even  the  more 
obviously,  however,  does  their  psychological  explanation 
fall  under  the  laws  of  that  theory  of  visual  perception 
which  we  are  illustrating. 

The  peculiar  perception  of  luminosity  which  a  slightly 
ruffled  sheet  of  water  has,  is  due  to  such  a  struggle  between 
the  two  fields  of  vision  of  the  two  eyes  as  results  in  a  rapid 
alternation  of  the  white  and  gray  images.  It  may  be  pro- 
duced by  combining  two  stereoscopic  pictures  of  like  con- 
tour, but  one  of  which  is  black  with  white  lines  and  the 
other  white  with  black  lines. 

Certain  optical  illusions  of  motion,  moreover,  involve 
very  obscure  and  complicated  applications  of  these  and 
other  physiological  principles  to  the  centres  of  the  brain. 
For  example,  in  watching  a  fall  of  water  for  a  long  time, 
the  steady  succession  of  images  passing  over  the  retina 
sometimes  ceases  to  be  perceived  as  a  motion  at  all.  The 
images  of  a  stationary  body  on  the  same  retinal  region  may 
appear  to  be  moving  in  the  opposite  direction.  In  certain 
cases,  even  the  sUme  elements  of  the  retina,  when  stimu- 


PERCEPTION    BY   THE   SENSES.  355 

lated  simultaneously,  may  give  rise  to  impressions  both  of 
motion  and  of  rest.  For  errors  of  visual  perception  like 
these,  unknown  laws  of  cerebral  action  need  to  be  assumed. 
The  data,  in  the  form  of  sensation-complexes,  and  revived 
and  associated  memory-images,  are  so  complicated  and 
thoroughly  fused  that  they  scarcely  admit  as  yet  of  a  satis- 
factory psychological  analysis. 

THE  DEVELOPMENT  OF   VISUAL  PERCEPTION. 

We  have  now  seen  what  are  the  "  sense-data  "  which  the 
mind  has,  as  it  were,  at  its  disposal  for  the  construction  of 
spatial  perceptions  by  sight  ;  and,  also,  what  are  the  more 
important  psycho-physical  laws  followed  in  the  process  of 
construction.  Visual  space  implies  coherent  complexes  of 
light-  and  color-sensations  systematically  arranged.  The 
arrangement  involves  native  activities  of  the  mind  in  de- 
pendence upon  the  action  of  the  bodily  mechanism  of  sense. 
But  it  also  implies  mental  growth,  development  under  the 
influence  of  experience.  Perhaps  we  may  rather  say  that 
the  development  of  visual  perception  is  the  organization  of 
certain  sensation-complexes,  arising  on  occasion  of  the 
activity  of  the  organ  of  vision,  into  a  visual  experience. 

It  is,  indeed,  difficult  if  not  impossible  to  tell  just  where 
the  limits  must  be  drawn  between  what  is  native  and  what 
is  learned.  There  can  be  no  doubt,  however,  that  seeing 
colors  (or  having  observed  localized  or  wholly  unlocalized 
sensation-complexes  of  light  and  color)  is  a  far  more  sim- 
ple and  primary  activity  than  seeing  colored  surfaces.  The 
perception  of  such  surfaces  —  of  a  system  of  light-  and  color- 
sensations  related  to  each  other  as  side  by  side  in  space- 
form  —  results  in  experience  from  the  fusion  or  weaving 
together  of  several  spatial  series  of  sensation-complexes. 
It  involves  muscular  and  tactual  sensation-complexes 
caused  by  the  motions  of  the  eye  for  parallel  turning,  for 
accommodation,  and  for  convergence. 


UNIVERSITY 
\\   /^  . 


356  PHYSIOLOGICAL  PSYCHOLOGY. 

But  the  visual  perception  of  extended  objects,  as  adult 
experience  possesses  it,  requires  binocular  vision  with  mov- 
ing eyes.  The  firm  spatial  connection  of  all  the  parts  of 
the  field  of  vision  requires  that  a  system  of  lines  of  direction 
should  be  fixed.  These  prescribe  the  objective  points  at 
which  the  sensations  produced  by  exciting  together  the  dif- 
ferent pairs  of  the  covering  points  of  the  two  retinas  must 
appear  in  visual  space.  To  establish  such  spatial  connec- 
tion, both  eyes  must  move  in  their  joint  action  as  a  single 
organ  of  vision.  Thus  the  field  of  binocular  vision  is  built 
up  by  an  order  of  experience  which  consists  in  the  succes- 
sive mastery  of  more  and  more  complex  problems. 

The  visual  perception  of  depth  involves  a  later  and  more 
complex  training  as  the  result  of  experience  than  the  per- 
ception of  two-dimensioned  extension.  To  solve  the  prob- 
lem of  depth,  binocular  vision  with  moving  eyes  —  thus 
calling  forth  the  muscular  sensations  that  accompany  con- 
vergence, and  the  resulting  combination  and  separation  of 
the  double  images  —  is  necessary.  Here,  too,  the  presence 
and  assistance  of  the  so-called  "  secondary  helps "  are 
extremely  important.  Thus  a  knowledge  of  the  solidity 
and  distance  of  objects  is  developed.  But  this  more  com- 
plex experience,  when  once  obtained,  modifies  completely 
what  is  really  more  simple  and  elementary.  What  we  see 
of  solid  and  distant  objects  with  one  motionless  eye,  de- 
pends upon  what  we  have  learned  to  see  with  both  eyes  in 
varied  motion  and  reliance  also  upon  all  the  available 
secondary  helps.  The  apparent  "  immediateness,"  or  natu- 
ral and  "  intuitive  "  character,  of  the  construction  of  the 
field  of  sight  in  monocular  vision  is  one  of  the  many  illu- 
sions with  which  the  evolution  of  all  our  experiences  is 
interpenetrated. 

These  general  remarks  apply  to  the  following  special 
topics  connected  with  the  development  of  visual  percep- 
tion. 


PERCEPTION  BY  THE  SENSES.          357 

Vision  of  Things  Upright  and  in  Correct  Spatial  Relations. 
—  Among  the  psychological  puzzles  often  propounded  as 
though  they  were  of  especial  difficulty  we  may  notice  the 
following :  Why  do  we  see  the  upper  part  of  the  object  by 
means  of  the  lower  part  of  the  retinal  image,  and  vice  versa? 
and,  Why  do  we  see  the  right  side  of  the  object  by  means 
of  the  left  side  of  the  retinal  image,  and  vice  versa  f  In 
other  words,  why  do  we  see  the  external  thing  with  its 
parts  up  and  down,  and  right  and  left,  exactly  the  reverse 
of  the  parts  of  the  image  ?  To  such  questions  the  right 
theory  of  visual  perception  and  its  development  offers  a 
ready  reply.  Strictly  speaking,  we  do  not  see  either  the 
retinal  image  or  the  extra-mental  material  thing.  The  field 
of  vision  is  a  subjective  affair,  and  is  like  neither  of  these 
two.  Perception  is  indeed  dependent  upon  the  formation 
of  the  retinal  image  as  one  occurrence  in  a  chain  of  physi- 
cal changes  ;  and  the  formation  of  the  image  is,  in  the  same 
way,  dependent  upon  the  action  of  the  rays  of  light 
reflected  from  the  object :  but  the  object  seen  is  not  a  copy 
of  either  image  or  extra-mental  thing. 

The  field  of  vision  gains  a  locality  in  objective  space 
only  as  we  develop  our  knowledge  of  the  relations  which 
our  entire  body  and  its  different  parts  sustain  to  the  earth 
and  to  the  different  things  surrounding  us.  The  use  of 
such  terms  of  position  as  "  up  "  and  "  down,"  or  "  right " 
and  "  left,"  implies  such  knowledge.  The  massive  feelings 
arising  from  the  condition  of  the  skin,  muscles,  joints,  and 
fluids  of  the  body,  keep  us  informed  of  our  general  rela- 
tions to  the  earth  and  to  objects  on  its  surface.  The  head 
is  the  upper  part  of  the  body,  or  part  farthest  away  from 
the  ground ;  the  feet  are  the  lower  parts,  in  contact  with 
the  ground.  When  the  eyes  move  downward,  the  lower 
parts  of  the  body  and  objects  situated  on  the  ground  come 
successively  into  the  field  of  vision ;  but  when  the  eyes 
are  moved  upward,  these  parts  successively  disappear  from 


358  PHYSIOLOGICAL   PSYCHOLOGY. 

the  field  of  vision.  "  Right "  is  the  direction  in  which  the 
eyes,  on  moving,  find  the  right  hand  and  objects  on  its 
side ;  and  "  left "  is  the  direction  in  which  the  eyes  look 
for  the  left  hand  and  for  objects  contiguous  to  it. 

Joint  Action  of  Eye  and  Hand.  —  These  two  organs  of  the 
body,  from  the  very  beginning  to  the  end  of  life,  are  con- 
stantly assisting  each  other  in  the  work  of  perception.  An 
almost  continuous  process  of  translation  is  taking  place 
between  the  two.  What  is  true  in  such  a  high  degree  of 
the  eye  and  the  hand  is  true  in  less  degree  of  the  eye  and 
all  the  members  of  the  body  of  whose  spatial  dimensions 
and  relations  visual  images  can  be  correctly  formed.  So 
also  in  our  perception  of  external  things  the  eye,  on  the 
one  hand,  and  the  tactual  and  muscular  organs,  on  the  other 
hand,  aid  each  other  in  the  work  of  localizing. 

Experiments  have  been  undertaken  to  show  the  degree 
of  accuracy  which  can  be  attained  in  translating  percep- 
tions between  the  eye  and  the  skin  and  muscles.  Bonders 
made  use,  for  this  purpose,  of  a  very  small  induction-spark 
which  was  to  be  touched  with  the  index-finger.  In  fifty 
experiments,  made  for  distances  of  60  to  610  mm.,  along 
the  same  line  of  regard,  in  perfectly  dark  surroundings, 
the  distance  was  estimated  right  four  times,  overestimated 
34  times,  underestimated  12.  The  greatest  errors  were 
+  35  and  -  34  mm.  When  the  surroundings  were  visible, 
the  spark  seen  with  open  eyes,  and  then  estimated  by  the 
finger  with  closed  eyes,  the  errors  were  reduced.  Local- 
izing in  this  way,  with  the  object  out  of  the  line  of  regard, 
was  much  more  inaccurate. 

Experiments  have  also  been  made  to  test  the  relative 
accuracy  with  which  the  three  perceptive  organs  —  eye, 
hand,  and  arm  —  will  receive  perceptions  of  distance  from 
each  other  and  translate  them  into  their  own  terms  of 
expression.  Jastrow  thus  concluded  that,  when  the  eye 
is  both  the  receiving  and  the  expressing  sense,  lengths  less 


PERCEPTION  BY  THE  SENSES.          359 

than  about  38  mm.  are  underestimated,  and  lengths  greater 
are  exaggerated.  But  when  the  hand  is  both  the  receiving 
and  expressing  organ,  lengths  less  than  about  50  mm.  are 
exaggerated,  and  lengths  greater  underestimated.  The 
arm,  in  expressing  all  lengths  received  from  the  eye,  exag- 
gerates them;  but  it  underestimates  all  lengths  received 
from  the  hand. 

Let  us  suppose  a  person  to  stand  blindfold  before  a  ver- 
tical table  and  make  with  one  hand  an  excursion  of  definite 
length  along  a  thread,  —  moving  at  the  same  time,  by  will, 
and  unguided  by  any  thread,  the  other  hand  to  the  amount 
supposed  to  represent  the  same  length.  If  the  unguided 
hand  starts  from  a  point  higher  up  than  the  other  and 
moves  upward,  it  moves  less  than  it  should  do ;  if  it  moves 
downward,  it  moves  more  than  it  should  do. 

All  such  results  as  the  foregoing  show  plainly  that  the 
interpretation,  back  and  forth,  of  visual  and  muscular  dis- 
tance is  a  matter  of  very  complex  development,  and  is  at 
best  only  imperfectly  attained.  It  is  not  possible  to  an- 
nounce any  one  principle  which  will  explain  all  the  errors  so 
persistently  committed  in  this  kind  of  interpretation.  We 
believe,  however,  the  following  two  principles  are  chiefly 
influential. 

In  the  first  place,  each  sense,  when  expressing  its  esti- 
mate of  perceptions  received  from  itself  or  from  another 
sense,  tends  to  approximate  the  dimensions  which  it  is 
accustomed  to  judge  most  accurately.  In  the  second  place, 
in  all  such  work  of  translation,  memory-images  of  visual 
perception  are  the  guiding  and  dominating  factors.  For 
example,  even  when  moving  about  in  the  dark,  in  a  familiar 
room,  we  carry  a  memory  sight-picture  of  the  position  of 
the  objects  in  the  room,  as  well  as  of  the  size  and  shape 
of  the  room,  to  guide  our  muscular  and  tactual  activity. 
When  we  try  by  arm  and  hand  to  indicate  the  position  of 
any  member  of  our  own  bodies,  or  of  any  external  object, 


360  PHYSIOLOGICAL  PSYCHOLOGY. 

« 

we  are  accustomed  to  make  our  estimate  first  in  terms  of 
memory-images  of  sight,  and  then  translate  through  the 
medium  of  these  images  into  the  required  "expressing" 
sense. 

In  closing  this  subject,  attention  should  be  directed  to 
the  limitations  of  explanation  with  which  the  science  of 
physiological  psychology  everywhere  finds  itself  encom- 
passed. One  of  these  limitations  is,  of  course,  reached  so 
often  as  we  are  obliged,  in  offering  our  explanations,  to 
recur  to  the  "  natural "  or  "  native  "  or  "  intuitive  "  opera- 
tion of  the  mind.  Nor  will  the  penetrating  student  of 
perceptive  processes  imagine  that  any  historical  or  experi- 
mental description  which  can  be  given  of  such  processes 
will  explain  the  origin  of  so-called  "  space  "  as  a  mental 
form  of  activity.  The  study  of  the  processes  emphasizes 
the  conclusion  that  the  space-form  of  all  perception  is 
mental;  it  is  not  a  copy,  or  representative,  of  ready-made 
£otfro-mental  existences  called  "things."  And  we  only 
anticipate  a  conclusion  warranted  by  our  entire  science 
when  we  repeat :  The  field  of  vision  is  a  subjective  affair, 
and  so  is  the  field  of  touch.  The  same  psychical  subject 
which  reacts  upon  the  stimulation  of  the  nervous  elements, 
in  the  form  of  various  quantitatively  and  qualitatively 
different  sensation-complexes,  constructs  by  its  synthesiz- 
ing activity,  in  the  development  of  its  own  life,  all  the 
so-called  "  objects  of  sense." 


CHAPTER  XV. 

TIME-RELATIONS   OF  MENTAL  PHENOMENA. 

SINCE  the  work  of  Bonders  in  1868,  no  single  subject 
in  the  general  study  of  mind  —  with  the  possible  exception 
of  Weber's  law  —  has  made  such  a  large  collection  of  sta- 
tistical data  as  that  known  by  the  title  "  psychometry." 
The  aim  of  this  branch  of  experimental  psychology  is  to 
determine  exactly  the  time-relations  of  mental  phenomena. 
If  the  results  are  to  be  estimated  by  the  number  and 
novelty  of  the  principles  established  beyond  doubt,  they 
must  be  admitted  to  be  remarkably  small.  Countless  trials, 
and  innumerable  tables  of  statistics,  from  which  already 
familiar  generalizations  (if  any  generalizations  whatever) 
are  somewhat  ostentatiously  derived,  thus  far  comprise  the 
chief  treasures  of  the  science  of  psychometry.  The  amount 
and  hopefulness  of  the  work  accomplished,  as  well  as  some 
promise  of  intrinsically  important  results,  require,  however, 
that  the  subject  should  receive  a  brief  treatment. 

Method  of  Experiment.  —  The  general  problem  in  all 
classes  of  trials  under  this  head  is  essentially  the  same. 
It  is  the  accurate  measurement  of  the  interval  which 
elapses  between  peripheral  stimulation  of  a  certain  organ 
of  sense  and  some  form  of  resulting  motion,  such  as  sig- 
nifies that  more  or  less  complicated  physiological  and 
psychical  processes  have  intervened.  The  electrical  cur- 
rent is  ordinarily  used  to  mark  the  precise  instants  when 
this  interval  begins  and  when  it  terminates.  The  stimulus 
may  consist  in  the  flash  or  crackle  of  an  electric  spark,  in 
the  sounding  of  a  bell  or  a  falling  ball  or  a  musical  note, 

361 


862  PHYSIOLOGICAL   PSYCHOLOGY. 

in  the  appearance  of  one  or  more  colors  or  figures,  or 
letters  or  words,  etc.;  and  the  resulting  motion  may  be 
with  the  finger  pressing  a  key,  with  the  foot  or  hand 
closing  or  breaking  a  circuit,  with  the  vocal  organs  calling 
into  a  tube,  etc.  All  such  experiments  may  be  repeated 
upon  many  persons,  an  indefinite  number  of  times,  and 
under  every  conceivable  variety  of  conditions  and  circum- 
stances. 

The  difficult  and  valuable  part  of  all  experiments  in 
psychometry  is  the  analysis  of  the  complex  cerebral  and 
psychical  factors  implied  in  the  processes.  The  difficulty  of 
this  analysis  is  due  to  the  speed,  complexity,  and  subtle 
variability  of  the  processes  which  are  to  be  analyzed.  The 
value  of  the  analysis  —  if  it  can  be  satisfactorily  accom- 
plished —  depends  upon  the  hope  of  discovering  what  are 
the  nature  and  the  relations  in  time  of  our  mental  pro- 
cesses, and  what  the  nature  of  their  dependence  upon 
processes  in  the  nervous  system. 

Simple  Reaction-time.  —  The  point  of  starting  in  all  ex- 
periment to  determine  the  time-relations  of  mental  phenom- 
ena is  the  fixing  of  "simple  reaction-time."  The  entire 
interval  between  the  instant  when  the  stimulation  of  the 
organ  of  sense  takes  place  and  the  instant  of  the  resulting 
movement  of  some  member  of  the  body  is  called  "  reaction- 
time"  (sometimes  "physiological  time").  Reaction-time 
is  simple  when  everything  which  tends  to  complicate  the 
processes,  and  so  to  lengthen  the  interval  between  stimu- 
lation and  motion,  has  been  eliminated.  Simple  reaction- 
time  is  obtained  in  response  to  a  single  sensation  of  known 
quality,  the  instant  of  whose  appearance  is  expected,  by 
executing  a  single  natural  and  accustomed  movement. 

But  the  simplest  reaction-time  is,  in  fact,  a  very  complex 
affair.  It  involves,  of  necessity,  not  less  than  seven  ele- 
ments :  (1)  An  action  of  the  stimulus  on  the  end-organ  of 
sense ;  (2)  centripetal  conduction  in  the  nerve ;  (3)  the 


TIME-RELATIONS   OF   MENTAL   PHENOMENA.          363 

same  in  the  spinal  cord  and  lower  parts  of  the  brain; 
(4)  transformation  of  the  sensory  into  the  motor  cerebral 
process;  (5)  centrifugal  conduction  in  the  lower  brain 
and  cord ;  (6)  the  same  in  the  motor  nerve ;  (7)  setting- 
free  of  the  muscular  motion. 

Psycho-physical  Time.  —  Of  the  seven  foregoing  processes 
involved  in  reaction-time  the  one  numbered  (4)  is  much 
the  most  interesting  to  physiological  psychology.  It  is 
called  "  psycho-physical  time  "  and,  in  its  more  elaborate 
form,  has  been  analyzed  by  Wundt  into  three  psycho- 
physical  factors :  these  are,  as  described  after  an  analogy 
derived  from  the  sense  of  sight,  (1)  entrance  into  the  field 
of  consciousness,  issuing  in  "  perception  "  ;  (2)  entrance 
into  the  point  of  clear  vision  in  consciousness,  issuing  in 
"  apperception  "  (i.e.  clear  and  attentive  perception)  ;  and 
(3)  the  excitation  of  the  "will,"  which  sets  free  in  the 
central  organ  the  registrating  movement.  For  each  of 
these  factors  time  is  required.  Each  of  them  is  psycho- 
physical,  —  that  is,  each  comprises  physiological  processes 
in  the  central  organs  and  simultaneous  corresponding 
changes  in  consciousness.  Given,  as  the  result  of  a  suffi- 
cient amount  of  experimenting,  the  average  simple  reac- 
tion-time, the  problem  becomes :  to  find  the  three  factors 
of  psycho-physical  time  (namely,  "  perception-time,"  "  ap- 
perception-time "  or  .discernment-time,  and  "  will-time  "), 
for  all  possible  conditions  and  degrees  of  complexity  and 
delay  of  the  psycho-physical  processes. 

Effect  of  Inertia.  —  Since  the  nervous  system  is  com- 
posed of  related  material  elements,  we  should  expect  that 
some  time  would  be  absorbed  in  realizing  the  effect  of  stim- 
ulation as  an  activity  of  the  different  organs.  We  should 
also  expect  that,  when  once  excited,  the  effects  of  the  ex- 
citement would  continue  for  some  time  after  the  stimulation 
has  ceased.  It  is  difficult,  however,  to  demonstrate  the  truth 
of  our  expectations  in  the  case  of  the  motor  nerve.  The 


364  PHYSIOLOGICAL   PSYCHOLOGY. 

nerve  does  not  seem  to  require  that  period  of  latent  excita- 
tion (about  T^  sec.)  which  the  muscle  requires  for  action 
under  the  influence  of  electricity.  The  case  of  the  end- 
organs  is,  however,  more  clearly  denned  by  experiment. 
These  organs  are  capable  of  receiving  only  about  so  many 
separate  excitations  in  a  given  unit  of  time.  The  number 
of  such  separate  excitations  is  different,  however,  for  dif- 
ferent senses ;  it  depends  also  upon  the  quantity  and 
quality  of  the  stimulus  used,  upon  the  place  of  its  appli- 
cation, etc.  More  than  a  certain  number  of  applications 
of  the  stimulus  to  an  end-organ  of  sense  results  in  fusion 
of  the  otherwise  successive  sensations. 

Smallest  Interval  for  Sensation  of  Touch.  —  The  results  of 
experiment  to  discover  the  greatest  promptness  with  which 
the  organ  of  touch  will  act  —  or,  in  other  words,  the  small- 
est interval  possible  between  two  separable  sensations  pro- 
duced by  repeated  stimulation  of  the  skin  —  differ  very 
greatly.  One  experimenter  has  placed  the  limit  at  27.6- 
36.8  nervous  shocks  per  second ;  another  at  480-640 ; 
another  at  about  1000. 

Smallest  Interval  for  Sensations  of  Sound.  —  The  noise  of 
the  electric  spark,  heard  with  one  ear  only,  has  been  dis- 
tinguished at  intervals  of  only  0.00205  sec.  By  using  the 
click  of  a  revolving  toothed  wheel  the  interval  was  thought 
to  be  fixed  at  0.016  sec.  It  is  increased  to  about  0.064 
when  the  sounds  are  heard  with  both  ears.  Of  course,  far 
fewer  musical  sounds  can  be  heard  in  the  same  amount  of 
time,  since  a  considerable  part  of  a  second  must  be  con- 
sumed before  the  tone  is  established,  as  it  were.  The 
number  of  separate  sensations  of  sound  possible  under  the 
most  favorable  circumstances  may,  then,  be  placed  at  about 
500  per  second. 

Smallest  Interval  for  Sensations  of  Sight.  —  In  ordinary 
daylight,  rotating  disks,  whose  surface  is  part  white  and 
part  black,  become  gray  (that  is,  the  sensations  fuse)  when 


TIME-RELATIONS   OF   MENTAL   PHENOMENA.          365 

they  attain  a  motion  of  about  twenty-four  per  second. 
With  care,  under  favorable  circumstances,  the  stimuli  of 
light  sensations  may  be  kept  separate  at  only  about  -$-$  sec. 
If  one  stimulus  strikes  the  fovea  centralis  and  the  other 
a  point  of  the  retina  6  mm.  off,  the  smallest  interval  for 
distinct  perception  becomes  about  0.076  sec. 

If  the  inertia  of  the  eye  for  different  color-sensations 
were  very  different,  objects  would  be  seen  of  varying  color 
according  to  the  time  during  which  the  rays  from  them 
acted  on  the  retina.  But  the  smallest  interval  for  the  per- 
ception of  different  colors  is  only  very  slightly  different. 
Recent  experiments  to  determine  the  length  of  time, 
expressed  in  0.001  sec.,  which  is  required  to  distinguish 
each  color  exposed  from  a  correspondingly  bright  shade 
of  gray,  yielded  the  following  mean- values :  Red,  1.28 ; 
orange,  0.82 ;  green,  1.42 ;  blue,  1.21 ;  violet,  2.32.  From 
these  results  the  principle  was  generalized  that  "  the  time 
colored  light  must  work  on  the  retina,  in  order  that  it 
may  be  seen,  increases  in  arithmetical  progression  as  the 
intensity  of  the  light  diminishes  in  geometrical  proportion." 
This  time  probably  represents  inertia  of  the  brain  and  nerve- 
tracts  as  well  as  of  the  retina. 

For  the  other  senses  —  smell  and  taste  —  the  measure- 
ment of  the  smallest  interval  is  too  inaccurate  to  admit  of 
satisfactory  discussion. 

Smallest  Interval  from  One  Sense  to  Another.  —  The  time 
required  for  discrimination  of  successive  sensations,  when 
they  belong  to  different  senses,  is  even  more  variable.  It 
depends,  of  course,  upon  the  two  senses  between  which 
the  discrimination  is  made,  upon  the  intensity  of  the  sen- 
sations compared,  upon  which  of  the  two  sensations  fol- 
lows the  other,  etc.  For  example,  the  average  interval 
between  sight  and  touch  (sight  following)  is  given  at 
0.05  sec. ;  between  sight  and  hearing  (sight  following) 
at  0.06  sec. ;  between  sight  and  touch  (sight  preceding)  at 


366  PHYSIOLOGICAL  PSYCHOLOGY. 

0.071  sec. ;  between  sight  and  hearing  (sight  preceding) 
at  0.16. 

Mean-values  of  Reaction-time.  —  As  has  been  already  seen, 
the  point  of  starting  in  all  experiments  in  psychometry  is 
the  determination  oi  simple  reaction-time.  But  the  value 
of  this  factor  varies,  by  smaller  or  larger  degrees,  with 
different  individuals,  and  with  the  same  individual  under 
different  circumstances.  By  repeated  experiments,  under 
the  most  favorable  conditions,  the  time  absorbed  by  the 
sensory-motor  cerebral  processes  is  reduced  as  nearly  as 
possible  to  zero.  The  mind  is  then  said  to  act  as  nearly 
as  possible  in  a  purely  mechanical  way  under  the  influence 
of  training  and  habit.  Even  then  the  simple  reaction- 
time  of  different  individuals  is  markedly  different.  For 
example,  from  "hand  to  hand"  (that  is,  one  hand  being 
hit  by  an  electrical  current  and  the  other  acting  to  press 
a  key)  the  reaction-time  as  given  by  different  experi- 
menters varies  from  about  0.1087  sec.  to  about  0.1911  sec. 
The  reaction-time  from  eye  to  hand  varies  from  about 
0.150  to  0.225  sec. ;  from  ear  to  hand,  0.120-0.182 ;  from 
neck  to  hand,  0.154,  etc. 

According  to  certain  authorities  the  reaction-time  for 
the  sensation  of  cold  is  somewhat  less  than  for  heat :  for 
example,  for  cold,  near  edge  of  eyelid,  0.135  sec. ;  upper 
arm,  0.150 ;  abdomen,  0.226  ;  inner  surface  of  thigh,  0.255  ; 
and  for  heat,  0.190,  0.270,  0.620,  and  0.790  respectively. 
Experiment  amply  confirms  the  familiar  experience  that 
the  contact  of  objects  is  much  quicker  perceived  than  their 
temperature. 

We  may  conclude,  then,  that  under  the  most  favorable 
possible  conditions  the  reaction-time  can  scarcely  be  reduced 
to  -^  sec.,  while  it  rarely  rises  much  above  -^  sec. 

Increased  Intensity  shortens  Reaction-time.  —  The  effect 
upon  the  reaction-time,  of  increasing  the  stimulus,  for  sen- 


TIME-RELATIONS   OF  MENTAL   PHENOMENA. 


367 


sations  of  sound  has  been  studied  by  Wuridt  with  the  fol- 
lowing result :  — 


Height  of  ball  falling. 
2  centimeters    .     . 

Reaction-time. 
Sec. 
.     .     .  0.161 

5  centimeters     .     . 

,     .     .  0.176 

.     .     .0159 

55  centimeters 

.  0.094 

Height  of  hammer  falling.      Reaction-time. 

Sec. 

1  millimeter 0.217 

4  millimeters 0.146 

8  millimeters 0.132 

16  millimeters  .  0.135 


Another  series  of  experiments  found  that  the  reaction- 
time  for  sensations  of  light  varied  from  0.251-0.308  to 
0.128-0.168,  according  to  the  intensity  of  the  stimulus  in 
six  degrees  of  strength.  Reaction-time  diminishes,  within 
certain  limits,  as  the  length  of  the  electric  spark  perceived 
increases. 

Expectation  shortens  Reaction-time.  —  If  a  preceding  sig- 
nal, at  a  favorable  interval,  informs  us  that  we  are  about 
to  be  called  upon  to  react,  the  time  necessary  for  reacting 
is  diminished.  The  cerebral  centres  are  thus  put  into 
that  condition  of  sensitiveness  to  stimulation  which  makes 
their  activity  the  promptest  possible.  Thus  the  interval 
necessary  for  perceiving  the  sound  caused  by  a  ball  falling 
25  ctm.,  which  without  signal  was  0.253  sec.,  was  reduced 
by  a  signal  to  0.076  sec. ;  and  when  the  fall  was  5  ctm.,  the 
interval  was  reduced  from  0.266  sec.  to  0.175  sec.  In  order 
to  secure  such  a  result,  however,  the  signal  must  not  be  dis- 
tracting ;  the  interval  between  it  and  the  expected  impres- 
sion must  be  nearly  constant,  and  not  so  long  as  to  over- 
strain attention. 

When  the  quality  of  the  impression  to  be  expected  is 
known,  but  its  intensity  is  unknown,  the  duration  of  reac- 
tion-time is  increased.  It  is  also  greatly  lengthened  when 
the  impression  takes  us  off-guard,  as  it  were ;  in  such  a 
case  the  reaction-time  may  reach  0.4-0.5  sec.  Of  course, 
it  takes  longer  to  react  in  an  unnatural  or  unaccustomed 
way. 


368  PHYSIOLOGICAL  PSYCHOLOGY. 

Finding  of  "Discernment-time."  —  Bonders  and  his  pupils 
were  the  first  to  examine  the  speed  of  the  psychical  pro- 
cesses (or  "  psychical  reflexes,"  as  one  observer  calls  them ; 
i.e.  "reflexes  with  cognition  of  the  excitant"),  with  a 
view  to  determine  how  long  it  requires  to  recognize  one  of 
two  or  more  different  perceptions  of  sense.  To  solve  this 
problem  they  employed  several  methods,  not  all  alike  of 
unquestionable  value  and  accuracy.  All  the  methods 
reduce  to  this  one ;  namely,  to  find  the  length  of  reaction- 
time  when  discernment  without  choice  takes  place,  and 
subtract  from  it  the  simple  reaction-time.  This  experi- 
menter allotted  to  the  development  of  a  clear  perception 
of  sound,  in  his  own  case,  about  0.039  sec. 

A  particular  mode  of  determining  the  amount  of  time 
required  for  "  apperception,"  or  discernment,  was  proposed 
by  Baxt;  it  was  based  upon  the  principle  of  inertia  as 
applied  to  the  senses,  especially  of  sight.  Let  us  suppose 
some  image,  which  requires  discernment  for  its  interpreta- 
tion (e.g.  the  image  of  a  particular  color,  of  a  letter  or 
word,  or  of  a  simple  geometrical  figure),  to  be  thrown  upon 
the  retina,  and  this  image  succeeded  after  a  brief  interval 
by  the  image  of  a  bright  white  disk ;  then,  if  the  interval 
be  too  brief,  the  first  image  will  be  "  quenched,"  as  it  were, 
by  the  second,  and  "  apperception  "  will  not  take  place. 
As  might  be  expected,  it  was  found  in  this  way,  that  the 
"  discernment-time,"  or  u  apperception-time,"  depends  upon 
the  complexity  of  the  operations  required.  To  recognize 
three  letters  at  once  required  about  half  the  time  necessary 
to  recognize  five  or  six.  With  an  interval  of  0.0048  sec. 
between  the  two  excitations,  the  perception  of  the  first 
was  reduced  to  scarcely  a  trace  of  a  weak  shimmer ;  with 
an  interval  of  0.0096  sec.,  letters  appeared  in  the  shimmer  ; 
one  or  two  of  which  could  be  recognized  when  the  interval 
increased  to  0.0144.  The  discernment  became  clearer  with 


TIME-RELATIONS    OF   MENTAL   PHENOMENA.  369 

an  interval  of  0.0192 ;  at  0.0336  sec.  four  letters  could  be 
well  recognized ;  and  at  0.0432,  five  letters. 

The  method  of  Baxt  does  not,  however,  enable  us  to  fix 
the  absolute  value  of  discernment-time,  because  it  includes 
as  an  inextricable  factor  the  amount  of  time  used  up  in 
the  peripheral  nerves.  Besides,  we  have  no  means  of  esti- 
mating to  just  what  stage  a  psycho-physical  process  must 
have  advanced,  when  it  becomes  impossible  for  a  following 
strong  impression  to  overwhelm  it. 

Two  other  observers  (von  Kries  and  Auerbach)  have 
attempted  to  measure  discernment-time  by  a  method  known 
as  the  "  Bonders'  C-method."  In  the  use  of  this  method 
the  subject  of  the  experiment  attempts  to  answer  the  ques- 
tion :  How  long  time  passes  after  the  occurrence  of  a  stim- 
ulation before  I  know  the  precise  nature  of  the  result  in 
consciousness  ?  by  either  reacting  in  a  prescribed  way,  or 
else  by  refraining  from  reacting  at  all.  It  was  assumed 
(probably  incorrectly)  that  "  will-time "  is  not  involved 
in  the  decision  to  react  or  not  to  react.  From  the  whole 
reaction-time,  as  involving  the  answer  to  the  forego- 
ing question,  the  simple  reaction-time  was  subtracted ;  the 
remainder  was  held  to  be  the  time  involved  in  discernment. 
By  this  method  surprisingly  small  intervals  were  obtained : 
for  example,  for  discernment  of  the  direction  of  light, 
0.011-0.017  sec.;  for  localization  of  sound,  0.015-0.077 
sec. ;  for  discernment  between  two  colors,  0.012-0.034 
sec. ;  etc. 

The  figures  just  given  have  been  contested,-  both  on 
account  of  the  method  employed  and  on  account  of  the 
result  obtained.  It  must  be  admitted  that  both  method 
and  result  can  be  justified  only  on  the  supposition  that  we 
are  trying  to  determine  how  promptly,  under  the  influence 
of  training  and  habit,  one  may  learn  to  connect  a  pre- 
scribed movement  with  a  particular  form  of  sensuous 
impression.  Under  such  circumstances  the  time  required 


370  PHYSIOLOGICAL  PSYCHOLOGY. 

for  strictly  psycho-physical  processes  becomes  reduced  to  a 
minimum,  and  "  discernment "  as  a  conscious  process  of  dis- 
crimination largely  or  wholly  disappears. 

Still  another  method  has,  therefore,  been  employed  for 
disentangling  the  elements  of  this  complicated  problem. 
In  this  method  the  subject  of  the  experiment  is  warned 
when  to  expect  one  of  two  or  more  colors,  but  does  not 
know  which  one  to  expect ;  he  is  left  to  his  own  judgment 
to  determine,  and  to  signal  just  when  the  act  of  discern- 
ment is  completed.  The  mean  discernment-time,  as  derived 
from  a  large  number  of  experiments  with  two  color-sensa- 
tions, was  fixed  by  this  method  at  from  0.047  to  0.086  sec. 

We  may  affirm,  then,  that  the  average  amount  of  the 
interval  occupied  in  discernment  of  a  very  simple  char- 
acter, under  favorable  circumstances,  is  not  very  different 
from  that  given  by  Bonders.  It  varies,  when  there  is  no 
special  designed  complication  of  the  conditions,  from  0.03 
sec.,  or  even  less,  to  nearly  0.1  sec.  Recent  experiments, 
in  the  dark  and  quiet,  to  find  the  whole  reaction-time, 
including  discernment,  for  different  colors,  report  the  fol- 
lowing result :  for  red,  0.153-0.160  sec. ;  for  blue,  0.156- 
0.164  sec. ;  for  violet,  0.161-0.168  sec. 

Several  Causes  that  affect  Discernment-time.  —  To  discrim- 
inate the  intensities  of  two  sensations  is  a  relatively  lengthy 
process.  For  example,  when  requested  to  react  upon  the 
stronger  only  of  two  stimulations  of  the  sense  of  touch,  we 
require  more  time  than  to  tell  where  we  are  touched. 
When  reaction  follows  the  weaker  of  two  such  stimula- 
tions, the  discernment-time  may  rise  to  0.069  sec.  or  0.089 
sec.  In  discerning  between  two  simple  tones  of  different 
pitch,  reaction  follows  the  one  of  higher  pitch  more 
promptly.  In  general,  discernment-time  diminishes  as  the 
pitch  of  the  tone  rises ;  for  very  high  tones  it  nearly  reaches 
the  limit  required  for  hearing  the  noise  of  the  electric 
spark-  .This  is  due  to.  the  fact  that  some  15-20  vibrations 


TIME-KELATIONS    OF   MENTAL   PHENOMENA.          371 

are  necessary  in  order  to  define  the  pitch  of  any  tone.  To 
localize  a  spark  by  indirect  vision  requires  more  time  than 
by  direct  vision. 

An  apparently  true  and  important  difference  has  recently 
been  detected  between  two  equally  normal  methods  of 
reacting  when  experimenting  for  discernment-time.  In  the 
first,  the  attention  is  concentrated  upon  receiving  the 
expected  sensation,  and  every  tendency  "  to  get  the  motion 
ready,"  as  it  were,  is  carefully  avoided.  In  the  second 
method,  one  does  not  think  of  the  sensation,  but  concen- 
trates the  attention  upon  getting  ready  to  move.  The 
reaction  in  the  extreme  "  motor "  type  is  much  prompter 
than  in  the  sensory  type,  • —  in  the  proportion  of  about  the 
following  figures :  0.125,  0.137,  0.123  sec.,  to  0.223,  0.224, 
0.230  sec. 

Discernment-time  increased  by  Number  of  Objects.  —  Every 
one  knows  that  it  takes  longer  —  other  things  being  equal 
— clearly  to  apprehend  several  objects  than  only  one  object. 
In  trying  to  discern  one  of  four  colors  the  time  of  the 
corresponding  psycho-physical  processes  is  lengthened  to  as 
much  as  ^  or  even  y2^  sec.,  and  more.  In  apperceiving  fig- 
ures, however,  it  requires  little  longer  to  master  three  than 
one,  but  considerably  longer  to  master  four  than  three.  The 
obvious  reason  for  this  is  our  habit  of  grasping  numbers 
in  periods  of  three  each.  Moreover,  the  discernment-time 
for  the  different  letters  varies  somewhat  remarkably ;  but 
the  "  legibility  "  or  comparative  accuracy  of  the  quick  dis- 
cernment of  the  different  letters  varies  still  more. 

Finding  of  "Will-time."  —  If  we  admit  the  accuracy  of 
the  conclusions  reached  as  to  simple  reaction-time  and 
"  discernment-time "  so  called,  it  becomes  comparatively 
easy  to  answer  the  following  question :  How  long  does  it 
take,  under  different  circumstances,  to  set  free  a  voluntary 
impulse?  The  simple  reaction-time  (.72)  —  or  time  required 
when  the  nature  of  the  stimulus  is  known  and  the  mode  of 


372  PHYSIOLOGICAL  PSYCHOLOGY. 

reaction  fixed  the  same  for  all  cases  —  is  first  found.  The 
reaction-time  required  to  discern  clearly  one  of  two  or 
more  impressions,  and  to  announce  the  fact  in  some  way 
previously  determined  upon  (^cf),  is  then  found.  Finally, 
the  reaction-time  is  found  for  cases  where  there  is  involved, 
also,  a  choice  of  one  of  several  ways  of  reacting,  or  a  choice 
between  reacting  and  not-reacting  (Rdw).  If  Rd-R  gives 
the  discernment-time,  Rdw-Rd  will  give  "will-time." 

Experimenting  in  this  way,  one  observer  found  the  mean 
interval,  in  the  case  of  ten  persons,  required  for  the  set- 
ting-free of  definite  reaction  involving  a  choice  between 
two  possible  courses,  varied  from  0.024  to  0.155  sec.  If 
the  choice  were  one  of  ten  possible  courses,  —  for  example, 
the  selection  of  one  of  the  ten  fingers  with  which  to  react 
on  receiving  the  impression  corresponding  to  that  finger,  — 
then  the  will-time  reached  0.298-0.448  sec. 

Individual  Differences  of  Will-time.  —  If  the  curve  of  the 
variations  in  the  time  required  for  choice  by  different  per- 
sons, under  different  conditions,  be  plotted,  very  inter- 
esting personal  peculiarities  manifest  themselves.  In  gen- 
eral, these  peculiarities  are  increased,  as  the  complexity  of 
the  choice  rises  from  one  to  five  places ;  they  are  then 
diminished  as  the  complexity  rises  to  nine  or  ten  places. 
It  thus  appears  that  men  differ  more  in  the  speed  with 
which  they  can  choose  one  of  two  to  five  different  courses, 
than  one  of  nine  or  ten  different  courses. 

A  careful  survey  of  the  whole  field  of  experiment  and 
statistics  shows  that  it  is  not  possible,  as  yet,  to  analyze 
psycho-physical  time  into  its  elements,  with  a  perfect  confi- 
dence in  our  accuracy.  By  practice  and  by  arranging  all 
the  conditions  as  favorably  as  possible,  so-called  "  discern- 
ment-time "  may  be  reduced  almost  to  zero.  That  is  to  say, 
reaction-time,  including  what  was  once  "  discernment-time  " 
and  "will-time,"  may  be  diminished  so  as  to  be  little  or  no 
greater  than  simple  reaction-time.  This  accords  with  all 


TIME-RELATIONS   OF  MENTAL   PHENOMENA.          373 

our  experience  of  the  rate  of  speed  possible  to  acquire  in 
all  movements  of  the  body  in  skilled  work  or  in  the  arts. 
The  violin-player,  for  example,  can  learn  to  execute  the 
complicated,  discriminating  movements  of  a  trill,  at  sight, 
with  as  great  speed  as  the  most  simple  muscular  move- 
ments excited  from  the  cerebral  centres. 

Donders  assigned  almost  precisely  the  same  figures  (0.036 
sec.)  to  will-time  as  to  discernment-time  (0.039).  Under 
comparable  circumstances  the  two  elements  of  psycho- 
physical  time  are  probably  about  the  same.  But  there  is 
other  evidence  to  indicate  that  successive  acts  of  discern- 
ment may  attain  a  much  higher  rate  of  speed  than  is  possi- 
ble for  successive  acts  of  will. 

Correspondence  of  Time  Subjective  and  Objective.  —  How 
accurately  does  the  estimated  time-rate  of  consciousness 
correspond  to  the  movement  of  time  as  measured  by  objec- 
tive standards?  Some  general  impressions  on  this  point 
are  derived  from  all  our  experience  in  psychometrical 
experiments.  Thus  one  observer  notes  that,  in  a  series  of 
39  reactions  from  eye  to  foot  which  actually  had  a  mean 
interval  of  0.184  sec.,  the  reaction  was  felt  to  be  "  too 
slow  "  when  it  reached  0.199  sec.,  and  pronounced  "  very 
good  "  when  it  fell  below  0.178  sec.  The  mind  therefore 
appreciated  the  actual  interval  to  within  about  0.01  sec. 

There  is  abundant  proof,  however,  that  the  speed  and 
duration  of  our  impressions,  as  estimated  in  consciousness, 
do  not  precisely  correspond  to  the  series  of  stimulations 
which  act  upon  the  organ  of  sense.  By  an  ingenious  de- 
vice Wundt  showed  that  one  rarely  hears  a  sound,  for 
example,  without  some  "positive"  (placing  it  later  than 
the  real  time)  or  "  negative  "  (placing  it  earlier  than  the 
real  time)  displacement  of  it.  When  expecting  a  sound, 
and  attempting  to  locate  it  in  connection  with  a  movement 
measured  by  the  eye,  the  displacement  is  most  frequently 


374  PHYSIOLOGICAL   PSYCHOLOGY. 

"  negative  "  ;  that  is,  one  believes  one  hears  the  sound  too 
soon  in  the  scale  of  visual  indications. 

Most  Favorable  Interval  for  Discernment.  —  The  degree  of 
accuracy  attainable  in  estimating  the  length  of  intervals 
varies  greatly  for  intervals  of  different  lengths.  There  is 
one  interval  most  favorable  of  all  for  exact  estimation. 
Under  ordinary  circumstances  our  sensitiveness  to  minute 
differences  of  time  is  greatest  at  about  0.7-0.8  sec.  (more 
precisely  0.71-0.755  sec.).  This  sensitiveness  to  minute 
differences  of  time  is  found  by  most  observers  to  fall  off 
quickly  for  intervals  less  than  the  most  favorable,  and 
more  slowly  for  intervals  greater  than  it;  and  this,  with 
the  result  that  times  longer  than  the  most  favorable  inter- 
val are  estimated  too  small ;  those  shorter,  too  large. 

On  applying  the  same  method  of  experimenting  to  con- 
siderably longer  intervals,  very  strange  and  somewhat  con- 
flicting results  are  obtained.  One  observer  finds  that  the 
maxima  of  accuracy  occur  at  the  intervals  which  are  mul- 
tiples of  the  most  favorable  interval  by  some  odd  number ; 
and  the  minima  of  accuracy  at  intervals  which  are  multi- 
ples of  the  most  favorable  interval  by  some  even  number, 
—  up  to  about  11.4  sec.  Another  observer  finds  that,  with 
0.7  sec.  taken  as  the  most  favorable  interval,  the  successive 
points  of  greatest  accuracy  are  2.8,  7.8,  9.3,  12,  and  14.2 
sec. ;  while  those  of  least  accuracy  are  5,  8.5,  10,  12.8,  and 
15  sec.  The  former  of  these  two  authorities  lays  down  the 
rule  that  minute  intervals  up  to  0.7  sec.  are  exaggerated, 
those  from  this  point  to  5  sec.  underestimated,  and  larger 
intervals  exaggerated  again.  But  another  authority  states 
that  times  shorter  than  2  sec.  are  overestimated,  and  those 
longer  than  4  sec.  underestimated.  It  is  obvious  that  indi- 
vidual peculiarities  are  likely  to  be  of  much  influence  in 
all  such  estimates ;  and  that  the  entire  subject  requires 
further  experiment  with  a  view  to  place  it  upon  a  basis  of 
broader  induction. 


TIME-RELATIONS   OF   MENTAL   PHENOMENA.          375 

Studies  in  Rhythm,  —  The  time-rate  of  the  most  rapid 
and  accurate  discernment  and  volition  may  be  profitably 
studied  by  determining  the  degree  of  accuracy  with  which 
successive  sensations  (like  the  clicks  of  clock-work),  having 
a  constant  interval,  can  be  counted.  In  this  way  it  has 
been  found  that  the  most  successful  estimates  cannot  be 
perfectly  sure  of  more  than  2-4  clicks,  when  the  interval 
between  them  is  as  brief  as  0.0895  sec. ;  and,  if  this  inter- 
val is  diminished  to  0.0523  sec.,  they  cannot  be  sure  of 
more  than  two  clicks.  The  most  successful  estimates  of 
45  rapidly  succeeding  sensations  were  42  and  43,  with  the 
longer  interval ;  with  the  shorter  interval,  the  best  estimate 
was  32,  the  worst  17. 

It  appears  then  that,  if  the  interval  between  the  sensa- 
tions counted  is  less  than  the  shortest  reaction-time  be- 
tween ear  and  tongue,  some  of  the  sensations  drop  out  of 
consciousness.  It  appears  also  that  the  rate  of  sensations 
may  far  exceed  the  rate  of  motor  impulses.  We  can  hear 
much  faster  than  we  can  count.  And,  in  general,  the  time- 
sense  for  series  of  mental  phenomena  is  different  for  differ- 
ent classes  of  these  phenomena. 

Reproduction  of  Composite  Images.  —  In  the  discernment 
of  one  or  more  letters,  numbers,  or  geometrical  forms, 
association  and  the  reproduction  of  mental  images  are,  of 
course,  involved.  In  fact,  no  discernment  is  possible  with- 
out involving  these  mental  processes.  It  is  interesting  and 
valuable,  however,  to  determine  how  the  reaction-time  is 
increased  by  complicating  these  processes.  This  may  easily 
be  done  by  fixing  the  mean  reaction-time,  including  these 
processes,  and  then  subtracting  the  mean  simple  reaction- 
time.  Thus  the  time  required  for  apprehending  single 
words  has  been  fixed  at  from  about  0.057  to  about  0.177, 
for  different  persons. 

All  our  familiar  experiences  concerning  the  differences 
among  different  individuals,  with  respect  to  promptness 


376  PHYSIOLOGICAL  PSYCHOLOGY. 

of  apprehension  and  memory,  concerning  the  conditions 
which  lengthen  or  shorten  these  processes,  etc.,  receive 
illustration  from  this  field  of  experiment.  The  following 
numbers  (which  must  be  taken  as  approximate  only)  prove 
this  statement. 

Sec. 

Time  needed  to  translate  images  into  one's  vernacular  .  0.477-0.545 
Time  needed  to  translate  images  into  a  foreign  language  0.649-0.694 
Time  needed  to  translate  short  familiar  words  ....  0.199-0.258 
Time  needed  to  translate  long  and  less  frequent  words  .  0.309-0.388 
Time  needed  to  remember  a  thing  very  well  known  .  .  0.400-0.800 
Time  needed  to  remember  with  choice  of  several  answers  0.222-1.042 
Time  needed  to  form  simple  and  familiar  associations  .  .  0.368-0.507 
Time  needed  to  form  odd  and  unexpected  associations  .  1.132-1.662 
Time  needed  to  form  a  simple  and  familiar  judgment  .  0.180-1.127 

Time  needed  to  define  a  familiar  word 0.391-2.023 

Time  needed  to  multiply  two  numbers  ..,,...  0.049-0.098 

[In  multiplying  two  numbers  we,  of  course,  call  upon 
an  extremely  familiar  and  well-fixed  association  gained 
when  we  learned  the  multiplication  table.  In  re-forming 
this  association,  however,  the  order  of  the  numbers  is  not 
a  matter  of  perfect  indifference;  reaction,  as  a  rule,  is 
quicker  and  more  correct  when  the  smaller  number  pre- 
cedes. It  is  also  somewhat  quicker,  in  most  cases,  when 
the  completion  of  the  process  is  announced  by  touching  $ 
key  with  the  finger  than  when  it  is  announced  by  uttering  a 
word  —  "reproduction  with  finger,"  instead  of  "reproduc- 
tion with  lip."] 

The  really  astonishing  thing  about  these  statistics  is  the 
very  great  difference  which  exists  in  different  cases  with 
respect  to  versatility  of  memory  and  promptness  of  decis- 
ion. This  fact  appears  when,  for  example,  the  subject  of 
the  experiment  is  called  upon  to  name  some  work  of  a 
well-known  writer,  some  city  in  a  particular  country  men- 
tioned to  him,  etc.  (utime  needed  to  remember  with  choice 
of  several  answers  ").  The  same  thing  is  illustrated  when 


TIME-RELATIONS   OF   MENTAL  PHENOMENA.          377 

he  judges  the  length  of  a  line  shown  to  him,  or  defines 
"  fame  "  as  "  a  form  of  the  ascription  of  praise,"  etc. 

The  Circuit  of  Consciousness.  —  Our  estimates  of  the  time- 
rate  and  duration  of  particular  factors  in  the  general  field 
of  consciousness  depends,  in  part,  upon  the  relation  which 
they  sustain  to  other  factors  in  the  same  field,  or  even  in 
the  field  which  has  just  faded,  as  it  were,  out  of  conscious- 
ness. Thus  the  general  principle  of  the  relativity  of  every 
state  and  of  every  factor  of  every  complex  state,  of  conscious- 
ness, is  amply  illustrated  by  experiments  in  psychometry. 

For  example,  when  words  are  connected  into  sentences, 
it  requires  only  about  one-half  as  much  time  for  each  word 
(as  0.138  sec.  to  0.484  sec.),  to  name  them,  as  would  be 
required  for  the  same  words  when  not  thus  connected. 
Single  letters,  too,  can  be  named  more  rapidly  when  sev- 
eral of  them  are  in  the  field  of  consciousness  together.  In 
nearly  all  cases  as  many  as  three  letters,  and  in  many  cases 
even  four  or  five,  lend  support,  as  it  were,  to  each  other.  It 
has  been  calculated  that  the  second  letter  in  view  shortens 
the  time  for  apperception  of  the  one  in  the  "  clear-spot "  of 
vision  by  about  -fa  sec-  5  even  the  fifth  letter  affects  favor- 
ably the  discernment  of  every  other  in  the  circuit  of  con- 
sciousness, to  about  the  amount  of  -^  sec. 

Another  application  of  the  same  principle  arises  in  the 
determination  of  the  number  of  impressions  which  can  be 
comprised  in  one  "  field  of  consciousness."  The  old-fash- 
ioned and  a  priori  theory  of  the  soul  decided  that,  on 
account  of  the  soul's  unity,  it  could  have  before  it  only 
one  object  at  the  same  instant  of  time.  Strangely  enough, 
the  most  advanced  school  of  associational  theorists  in  Eng- 
land has  maintained  the  same  view.  But  experiment  con- 
firms the  impression  of  the  plain  man's  self-consciousness. 
He  believes  that  he  can  attend  —  though  with  varying 
degrees  of  attentive  perception  —  to  several  objects  at  the 
same  time ;  and  he  can  do  what  he  believes  he  can. 


378  PHYSIOLOGICAL   PSYCHOLOGY. 

To  test  this  matter,  let  us  suppose  that  the  stroke  of  a 
pendulum,  heard  at  regular  intervals,  is  employed  as  the 
stimulus.  Two  series  of  successive  strokes,  separated  by 
an  interval,  are  compared  without  counting.  How  many 
impressions  can  such  series  contain  and  the  comparison 
attain  a  high  degree,  or  even  a  perfection,  of  accuracy? 
With  the  most  favorable  interval  (0.2-0.3  sec.)  between 
the  successive  impressions,  and  with  strict  attention,  most 
persons  can  attain  a  high  degree  of  accuracy  with  10  or 
12  impressions ;  some  can  hold  in  one  field  of  conscious- 
ness no  fewer  than  15  or  16  impressions.  If  rhythmic 
grouping  is  permitted,  the  groups  become  as  one  percep- 
tion, and  35  to  40  impressions  are  apprehensible  in  one 
field  of  consciousness.  It  is  thought  possible  by  some 
experimenters  to  apprehend  a  larger  even  number  than 
odd  number  in  the  circuit  of  consciousness. 

Or,  again,  let  us  try  to  determine  the  "grasp  of  con- 
sciousness "  by  showing  from  4  to  15  short  perpendicular 
lines  for  0.01  sec.,  and  then  testing  the  accuracy  of  the 
perception  possible  of  these  groups  of  objects.  By  experi- 
menting in  this  way  it  has  been  ascertained  that  most  per- 
sons are  infallible  when  groups  containing  not  more  than 
4-6  lines  are  displayed. 

Effect  of  Practice,  Attention,  and  Fatigue.  —  Every  one 
knows  that  practice  and  attention  increase,  and  fatigue 
diminishes,  the  speed  and  the  accuracy  of  our  mental  proc- 
esses. Psychometry  endeavors  exactly  to  define  the  amount 
of  these  influences  on  reaction-time.  Thus  it  has  been 
found  that  practice  reduces  about  one-third  (0.080  sec.  to 
0.050;  0.098  sec.  to  0.062,  etc.)  the  "will-time"  necessary 
for  choice  between  two  motions.  By  practice  with  five 
possible  choices,  the  reaction-time  fell,  in  one  case,  from 
0.239  sec.  to  0.083;  in  another  case,  where  one  of  ten 
choices  was  required,  the  time  was  diminished  from  0.358 
to  0.094.  The  effect  of  practice  on  discernment-time  is 


TIME-RELATIONS   OF   MENTAL   PHENOMENA.  379 

different.  It  may  fall  from  as  much  as  0.117  sec.  to  as 
little  as  0.021  sec.  Discernment-time  continues  to  decrease 
by  practice  after  all  diminution  of  simple  reaction-time 
has  ceased.  Association-time  is  probably  sensitive  to  prac- 
tice in  far  less  degree. 

The  effect  of  attention  on  reaction-time,  and  so  on  the 
psycho-physical  processes  involved,  shows  itself  in  a  marked 
way  when  attention  is  disturbed.  Thus  the  mean  reaction- 
time,  for  a  weak  impression  of  sound,  was  increased  by  a 
disturbing  noise  from  0.189  to  0.313  sec.;  and,  for  the  sight 
of  an  electric  spark,  from  0.222  to  0.300  sec. 

Fatigue  and  all  depletion  of  nervous  vigor  tends  to 
lengthen  the  period  of  reaction-time.  The  enervation  of  a 
hot  summer's  day,  of  a  sleepless  night,  or  following  on  bad 
news,  has  the  same  effect.  In  cases  of  idiocy,  imbecility, 
and  epilepsy,  the  length  of  psycho-physical  time  is  in- 
creased. The  simple  reaction-time  of  a  decrepit  man  of 
seventy-seven,  taken  from  the  almshouse,  was  found  at 
first  to  be  0.9952  sec. ;  practice  reduced  it  greatly,  but  not 
below  0.1866  sec.  The  appearance  of  sprightliness  does 
not,  however,  always  signify  a  speedy  and  accurate  per- 
formance of  the  psycho-physical  processes  involved  in  reac- 
tion. Of  two  young  men,  Exner  found  one  with  a  lively 
temperament  to  have  a  mean  reaction-time  of  0.3311  sec. ; 
while  the  other,  who  had  not  a  lively  temperament,  showed 
a  reaction-time  of  only  0.1337. 

Effect  of  Drugs,  Hypnotism,  etc.  —  The  nature  of  the 
influence  which  alcohol  has  upon  the  speed  of  the  psycho- 
physical  processes  is  not  quite  clearly  proved  by  experi- 
ment. Doubtless  it  differs  greatly  in  dependence  upon 
individual  peculiarities,  the  quantity  taken,  and  other  more 
obscure  conditions.  Some  observers  find  that  a  small  quan- 
tity of  wine  slowly  drunk  decreases  reaction-time ;  but  a 
larger  quantity,  in  several  cases,  increased  it  from  0.1904 
to  0.2969  sec.,  although  the  subject  of  the  experiment  con- 


380  PHYSIOLOGICAL  PSYCHOLOGY. 

sidered  himself  to  be  reacting  with  unusual  promptness.  A 
long  series  of  recent  experiments  (some  8000  in  all),  to 
determine  the  effects  of  alcohol,  ended  in  disappointment. 
They  appear  simply  to  have  showed  that  this  drug  pro- 
duces changes  in  reaction-time;  but  no  constant  effect 
dependent  upon  either  quantity  or  kind  could  be  detected. 

Coffee,  as  a  rule,  decreases  reaction-time,  beginning  its 
effect  some  20-25  minutes  after  being  taken  and  continuing 
it  for  about  two  hours.  Experiment  thus  appears  to  con- 
firm the  influence  of  this  drink  to  assist  a  certain  speed 
and  accuracy  of  psycho-physical  processes;  doubtless  (it 
should  be  added)  in  those  cases  only  where  it  is  moderately 
used  and  produces  no  disturbance  of  digestion.  Subcuta- 
neous injections  of  morphine  delay  reaction-time ;  but  the 
effect  soon  disappears  unless  the  injection  is  repeated. 

In  summing  up  the  results  of  experiment  we  should  be 
warned  against  imagining  that  researches  in  psychometry 
explain  the  origin  or  nature  of  our  ideas  of  time  and  of 
time-relations.  To  describe  the  rates  and  orders  and  dura- 
tions of  the  successive  ideas  is  a  very  different  thing  from 
explaining  the  idea  of  succession.  Upon  the  origin  and 
nature  of  this  idea  -the  so-called  science  of  psychometry 
throws  no  light.  Neither  has  it  as  yet  succeeded  in  estab- 
lishing new  principles  of  peculiar  value  in  psychology. 
We  shall  refer  to  some  other  of  its  more  important  rela- 
tions when  we  come  to  speak  of  the  psycho-physical  char- 
acter of  attention  and  "acts 'of  will"  so-called. 

One  important  thing  to  notice  is  that  the  different  ele- 
ments of  psycho-physical  time  —  such  as  discernment-time 
and  will-time,  and  time  necessary  to  come  to  consciousness, 
as  it  were  —  ordinarily  overlap  and  blend  with  each  other. 
But  practice  and  attention  tend  in  the  direction  of  reduc- 
ing them  all  to  zero ;  so  that  the  formerly  complicated 
case  comes,  under  these  influences,  to  assume  the  psycho- 
physical  character  and  duration  of  a  case  of  simple  reaction- 
time. 


CHAPTER   XVI. 
FEELINGS,  EMOTIONS,  AND  MOVEMENTS. 

SINCE  the  beginning  of  serious  attempts  to  establish  a 
scientific  psychology  the  consideration  of  the  feelings  and 
emotions  has  been  unsatisfactory.  The  reasons  for  this 
fact,  however,  are  partly  unavoidable,  for  they  lie  in  the 
nature  of  the  case. 

GENERAL   THEORY  OF  THE  FEELINGS. 

Regarded  from  the  introspective  point  of  view,  the  phe- 
nomena of  feeling  are  peculiarly  obscure,  indefinite,  vari- 
able, and  multiform.  The  very  effort  to  subject  them  to 
a  self-conscious  examination  immediately  changes  their 
entire  character  or  wholly  dissipates  them.  Their  physi- 
ological conditions,  also,  are  laid  in  equally  obscure,  rap- 
idly and  infinitely  varied  changes  of  the  central  organs 
of  the  nervous  system.  These  conditions  cannot  be  sub- 
jected to  direct  observation,  or  even  —  without  great  dif- 
ficulty—  to  the  more  indirect  methods  of  experimental 
analysis. 

It  is  not  surprising,  then,  to  find  that  physiological  psy- 
chology has  little  beyond  certain  more  or  less  well-founded 
conjectures  to  offer  respecting  this  department  of  investi- 
gation. 

Essential  Nature  of  Feeling.  —  Several  fundamentally  dif- 
ferent views  exist  as  to  the  essential  nature  of  the  mental 
phenomena  for  which  we  use  the  term  "feeling."  Indeed, 
the  term  itself  is,  as  a  rule,  vaguely  employed.  Sometimes 
it  means  the  sensation  of  pressure  or  of  temperature  local- 

381 


382  PHYSIOLOGICAL   PSYCHOLOGY. 

ized  in  the  skin  (e.g.  I  feel  the  smoothness  or  coolness  of 
the  marble) ;  sometimes  it  refers  to  sensation-complexes 
of  an  obscure  and  mixed  origin  and  character  (I  feel  tired, 
or  well,  or  ill  at  ease) ;  sometimes  it  designates  what  has 
been  called  more  definitely,  but  uncouthly,  "  the  pleasure- 
pain  series  " ;  sometimes  it  is  employed  for  states  of  ses- 
thetical  or  religious  contemplation ;  and  sometimes  for 
that  unique  recognition  which  the  mind  gives  to  •  moral 
obligation  (the  feeling  designated  by  the  words  "I  ought"), 
etc. 

In  general,  three  theories  must  be  recognized  as  to  the 
essential  Nature  of  Feeling.  One  of  these  emphasizes  the 
underiv.ed  and  primary  character  of  such  states  as  merit 
this  name.  It  claims  that  we  can  no  more  define  what  it 
is  "to  feel"  than  what  it  is  to  know.  Indeed,  it  would 
seem  to  be,  of  the  two,  more  unreasonable  to  require  a 
definition  of  feeling.  For  to  define  is  to  use  terms  of 
ideation ;  but  feeling,  as  such,  is  not  ideation  at  all,  and 
therefore  its  character  cannot  be  stated  in  terms  of  idea- 
tion. The  other  two  theories  agree  in  regarding  feeling  as 
a  secondary  or  derived  activity  of  the  mind.  But  one 
theory  is  physiological,  and  the  other  may  be  said  to  be 
44  ideational,"  in  its  method  of  explanation.  We  shall  pass 
these  two  theories  briefly  in  review  before  returning  to  the 
first-mentioned  and  —  as  we  believe  —  true  theory  of  the 
essential  nature  of  feeling. 

Physiological  Theories  of  Feeling.  —  These  theories  hold 
that  those  mental  states  which  we  call  "feelings "  are, 
essentially  considered,  a  peculiar  consciousness  of  the  condi- 
tion of  the  nervous  system.  That  many  states  of  feeling  are 
directly  dependent  upon  conditions  which  originate  in  the 
activities  of  the  nervous  elements ;  and  that  some  nervous 
conditions  are  followed  by  painful,  and  others  by  pleasur- 
able, feeling,  there  can  be  no  doubt.  It  is  very  difficult, 
however,  to  bring  all  of  the  physiological  conditions  of 


FEELINGS,   EMOTIONS,   AND   MOVEMENTS.  383 

feeling  under  any  verifiable  laws.  And  even,  should  we 
succeed  in  doing  this,  we  should  not  define  or  express  the 
essential  nature  of  feeling. 

Concord  between  Stimulus  and  Vital  Activity.  —  The  phil- 
osopher Lotze  distinguished  the  feelings,  as  mental  condi- 
tions involving  pain  or  pleasure,  from  sensations  as  indif- 
ferent elements  of  our  perception  of  things.  Pleasurable 
feelings  arise  from  coincidence,  and  painful  from  opposi- 
tion, between  the  effects  of  the  stimulus  and  any  of  those 
conditions  to  which  the  regular  expression  of  the  bodily  or 
spiritual  life  is  attached.  "  Feeling  is,  in  general,"  says 
Lotze,  "only  the  measure  of  the  partial  and  momentary 
concord  between  the  effect  of  the  stimulus  and  the  con- 
ditions of  vital  activity."  It  is  impossible,  however,  to 
vindicate  this  principle  as  applying  to  all  cases.  The 
disagreeable  character  of  the  slightly  bitter  tonic,  or  the 
pleasurable  sweetness  of  the  deadly  acetate  of  lead,  cannot 
be  declared,  on  scientific  grounds,  to  signify  even  "  a  par- 
tial and  momentary  "  discord  or  concord  between  stimulus 
and  vital  activity.  Lotze,  moreover,  was  far  too  keen  a 
psychologist  to  suppose  that,  in  laying  down  this  principle, 
he  was  explaining  feeling  as  a  secondary  form  of  conscious- 
ness. On  the  contrary,  he  himself  expressly  vindicated  its 
right  to  be  regarded  as  primitive. 

Relation  of  Feeling  to  Quantity  of  Sensation.  —  It  is  a  rule 
of  wide  application,  that  sufficient  intensities  of  all  forms 
of  stimuli  are  productive  of  painful  feeling.  The  same 
intensities  are  also,  in  general,  antagonistic  to  the  vital 
conditions  of  the  organism.  On  the  other  hand,  all  inten- 
sities of  some  sensations  of  smell,  taste,  and  hearing,  are 
disagreeable  to  most  persons.  Nor  can  the  disagreeable 
feelings  of  the  higher  intellectual,  ethical,  and  sesthetical 
order  be  resolved  into  the  consciousness  of  more  stimula- 
tion of  the  nervous  system  than  is  good  for  its  vital  inter- 
ests. The  excessive  and  injurious  stimulation  of  this 


384  PHYSIOLOGICAL  PSYCHOLOGY. 

system  may  be  accompanied  by  a  large  amount  of  positive 
pleasure.  Of  course,  in  all  these  cases,  attention,  associa- 
tion, habit,  and  voluntary  control,  have  much  to  do  with 
determining  the  subjective  state  occasioned  by  the  appli- 
cation of  the  various  degrees  of  stimulus. 

The  dependence  of  pleasurable  or  painful  quality  (or 
tone)  of  feeling  upon  the  amount  of  nervous  excitement 
produced  by  the  stimulus  is  most  apparent  in  the  case  of 
the  sensations.  Sensations  of  moderate  intensity  are 
usually  pleasurable ;  by  "  moderate  "  intensity  we  can 
scarcely  fix  anything  more  definitely  than  the  actual 
point  at  which  the  minimum  of  painful  feeling  begins  to 
follow  an  increase  in  stimulation.  From  this  point  the 
feeling  of  pain  rises  in  intensity,  as  the  intensity  of  the 
stimulus  increases.  But  the  curves  which  measure  the  in- 
crease of  feeling  and  the  increase  of  sensation  do  not  cor- 
respond. According  to  Wundt,  the  maximum  point  of 
pleasure  belonging  to  any  sensation  is  the  point  where  the 
sensation  ceases  to  increase  in  simple  proportion  to  the 
strength  of  the  stimulus. 

The  view  which  regards  painful  feeling  as  the  conscious- 
ness, so  to  speak,  of  the  over-stimulation  of  the  nervous 
organism,  is  compelled  to  deny  that  any  sensation  can  be 
painful,  absolutely,  or  irrespective  of  its  intensity.  Such 
denial  contradicts  tolerably  obvious  facts.  As  has  been 
said,  all  degrees  of  some  sensations  are  disagreeable  to 
most  persons.  To  point  to  the  fact  that  some  substances 
whose  faint  odor  (as  musk),  or  taste  in  moderate  degree 
(as  the  bitter  of  hops)  is  agreeable,  become  intensely  dis- 
agreeable when  they  excite  more  intense  sensations,  is  not 
conclusive.  The  faint  sensations  are  not  the  same  sensa- 
tions; their  quality  changes  on  increase  of  stimulus  as 
truly  as  their  quantity. 

View  of  Bain  and  Grant  Allen,  —  The  English  psycholo- 
gist Bain  has  laid  down  the  principle:  "States  of  pleasure 


FEELINGS,   EMOTIONS,   AND  MOVEMENTS.  385 

are  connected  with  an  increase,  and  states  of  pain  with  an 
abatement,  of  some,  or  all,  of  the  vital  functions."  This 
principle  has  been  criticised  as  "too  vague"  by  Grant 
Allen,  who  would  substitute  for  it  the  following :  "  Pleas- 
ure is  the  concomitant  of  the  healthy  action  of  any  or  all 
of  the  organs  or  members  supplied  with  afferent  cerebro- 
spinal  nerves,  to  an  extent  not  exceeding  the  ordinary 
powers  of  reparation  possessed  by  the  system."  But  this 
statement  (which,  in  principle,  is  similar  to  that  of  Lotze) 
seems  to  us  much  more  vague  than  that  which  it  is  in- 
tended to  replace.  For  what  satisfactory  standard,  besides 
the  cessation  to  produce  the  feeling  of  pleasure,  shall 
measure  the  limit  referred  to  in  the  words — "to  an  extent 
not  exceeding  the  ordinary  powers  of  reparation  possessed 
by  the  system."  Surely  it  requires  a  large  credulity  to 
believe  that  the  powers  of  repair  are  exceeded  whenever  a 
robust  man  experiences  a  slightly  disagreeable  taste,  or 
an  unpleasant  contrast  of  colors,  or  a  bit  of  a  twinge  of 
conscience. 

_  The  Herbartian  Theory  of  Feeling.  —  In  strong  contrast  to 
all  physiological  theories  stands  the  view  which  regards 
the  feelings  as  secondary  conditions  of  mind,  dependent  on 
the  relations  of  the  ideas.  This  view  makes  a  sharp  dis- 
tinction between  sensation  and  feeling.  It  classifies  bodily 
pain  as  sensation  and  not  as  feeling.  Hunger,  thirst,  weari- 
ness, shivering,  etc.,  are  sensations  and  not  feelings.  But 
sympathy,  love,  gratitude,  reverence,  admiration,  etc.,  are 
feelings ;  since  their  content  is  of  a  mental  rather  than  a 
physical  order.  The  author  of  this  view  was  the  German 
philosopher,  Herbart. 

Feeling  is,  therefore,  to  be  defined  (so  this  school  of 
psychologists  hold)  as  the  immediate  consciousness  of  the 
rising  and  falling  of  one's  power  of  ideating,  as  it  were. 
It  is  not  a  primitive  activity  of  mind ;  it  is  secondary  and 
results  from  the  reciprocal  action  of  the  ideas.  If  the 


386  PHYSIOLOGICAL   PSYCHOLOGY. 

ideas  "  inhibit "  each  other,  the  becoming  conscious  of  the 
check  or  inhibition  is  unpleasant;  if  they  "further"  each 
other  and  readily  fuse,  the  conscious  feeling  of  this  fact  is 
pleasant.  As  the  most  prominent  recent  representative  of 
this  view  teaches  (namely,  Volkmann  von  Volkmar) : 
"  Feeling  is  the  immediate  consciousness  of  the  process  of 
ideation  itself  as  distinguished  from  the  consciousness  of 
this  or  that  idea,"  and  it  is  conditioned  upon  some  resist- 
ance being  offered  to  the  process.  The  condition  of  the 
origin  of  a  feeling  is,  then,  the  existence  of  two  simulta- 
neous opposed  ideas ;  this  co-existence  occasions  a  state  of 
"  tension,"  and  this  state  gives  way  as  one  idea  triumphs 
over  another. 

The  theory  just  described  is  interesting ;  it  undoubtedly 
accounts  for  the  conditions  under  which  a  large  number 
of  our  pleasurable  or  painful  feelings  originate,  — especially 
those  of  the  higher  intellectual  and  sesthetical  order.  But 
to ^refuse  to  speak  of  pleasurable  and  painful  sensations 
and  emotions  as  belonging  to  the  realm  of  "feeling"  at 
all,  because  they  depend  upon  a  physical  basis,  is  to  restrict 
the  term  unwarrantably.  The  Herbartian  view,  as  a  com- 
plete account  of  the  nature  of  feeling,  is  disproved  by  all 
the  considerations  brought  forward  by  the  various  forms 
of  the  physiological  theories. 

Feeling  an  Original  and  Underived  Form  of  Consciousness. 
—  We  return  then  to  our  former  declaration.  Feeling  is 
a  primitive  and  underived  mode  of  the  operation  of  conscious 
mind.  It  can  neither  be  denned  by,  nor  deduced  from, 
processes  of  sensation  or  ideation.  To  know  what  it  is  to 
feel,  the  highest  intelligence  would  not  of  itself  be  capable. 
Such  knowledge  comes  only  from  having  felt.  And  feeling 
accompanies  all  mental  experience,  both  that  of  sensation 
and  that  of  the  higher  intellectual  processes.  Discrimina- 
tion—  which  is  an  intellectual  process— -is,  of  course, 
involved  in  all  recognition  of  the  distinctions  in  quality 


FEELINGS,    EMOTIONS,    AND   MOVEMENTS.  387 

of  the  different  feelings,  and  of  the  characteristic  tone  of 
pleasure  or  pain  which  they  all  (or,  in  case  we  admit  some 
"  neutral "  feelings,  nearly  all)  possess.  But  the  discrimi- 
nation of  quality  involves  the  existence  of  quality  to  be 
discriminated.  The  feeling  of  pleasure  we  have  in  smelling 
a  sweet  rose,  or  in  tasting  a  favorite  dish,  actually  differs 
in  quality,  as  well  as  in  amount  of  pleasure  characterizing 
its  place  in  the  so-called  "  pleasure-pain  series,"  from  the 
pleasure  of  doing  a  good  deed ;  otherwise  it  could  not  be 
known  as  different. 

Physical  Basis  of  Feeling,  —  That  many  of  our  feelings 
depend  immediately  upon  the  condition  of  the  nervous 
elements  is  beyond  doubt.  But  are  there  special  nervous 
elements  —  whether  end-organs,  nerve-fibres,  or  portions 
of  the  central  organs  —  which  must  be  excited  in  order  to 
give  rise  to  painful  feelings  ?  What  is  the  peculiar  nature 
of  the  excitation  upon  which  the  different  feelings  depend 
for  their  differences  of  quality  ?  What  is  the  characteristic 
change  in  the  excitation  that  gives  rise  to  the  two  kinds  of 
"  tone  "  which  the  feelings  possess,  —  to  pleasure  and  to 
pain  ?  Physiological  psychology  can  answer  none  of  these 
questions  with  much  confidence. 

The  prevalent  view,  hitherto,  has  probably  been  that  the 
same  nervous  apparatus  throughout,  which  on  moderate 
excitement  produces  sensations  of  pressure  or  temperature, 
produces  feelings  of  pain  when  irritated  with  increased 
intensity.  This  view  would  apparently  be  compelled  to 
hold  that  muscular  sensations  have  the  same  physical 
apparatus  as  feelings  of  muscular  weariness  or  exhaustion  ; 
and  that  both  hunger  and  cardialgia  arise  from  excitation 
of  the  same  nerves  of  the  stomach. 

Certain  reasons  exist,  however,  for  doubting  the  complete 
identity  of  the  nervous  apparatus  of  painful  and  pleasura- 
ble feeling  with  that  of  the  sensations  with  which  such  feel- 
ing is  allied.  Recent  experiments  seem  to  show  clearly 


388  PHYSIOLOGICAL   PSYCHOLOGY. 

that  the  end-organs  of  pressure,  temperature,  and  painful 
sensation,  are  not  the  same  (see  p.  237  f .).  It  is  probable  also 
that  impulses  resulting  in  pain  travel  by  more  or  less  dis- 
tinct paths  in  the  spinal  cord  (see  p.  71  f .).  In  certain  cases 
of  disease  the  sensibility  of  the  skin  to  pain  is  lost,  while 
its  sensibility  to  touch  is  not  weakened.  The  reverse  con- 
dition alsp  sometimes  occurs.  In  some  diseased  conditions 
a  difference  of  as  much  as  one  or  two  seconds  occurs  in  the 
time  at  which  the  sensations  of  contact  and  the  feelings  of 
pain  (caused — for  example  —  by  the  prick  of  a  needle) 
arise  in  the  mind.  The  painful  feeling  of  being  blinded, 
when  the  stimulus  of  light  is  too  intense,  seems  to  arise 
from  simultaneous  irritation  of  the  trigeminus,  rather  than 
from  the  same  irritation  of  the  optic  nerve  which  results  in 
sensations  of  light. 

The  tendency  of  recent  evidence  seems  to  be,  then, 
toward  a  somewhat  complete  separation  of  the  nervous 
mechanism,  whose  excitement  produces  feelings  of  sen- 
suous pain  or  pleasure,  from  that  whose  excitement  results 
in  the  production  of  the  sensations  themselves.  This  evi- 
dence favors,  so  far  as  physiological  theory  can,  the  view 
of  those  psychologists  who  regard  feeling  as  a  primitive 
and  underived  form  of  conscious  life. 

As  to  the  peculiar  nature  of  the  physiological  action  — 
whether  in  the  end-organs,  the  nerve-tracts,  or  the  nerve- 
centres —  which  results  in  conscious  states  of  feeling,  we 
have  no  information.  Indeed,  the  facts  just  referred  to 
are  very  difficult  to  reconcile  with  the  rule  which  certainly 
covers  a  large  number  of  cases,  —  namely,  that  increased 
intensity  of  stimulus,  beyond  a  certain  point,  results  in  the 
production  of  painful  sensations.  This  rule  itself  is  un- 
doubtedly due  to  inter-cerebral  relations  whose  physical  and 
physiological  description  science  cannot  give  at  present. 

Classification  of  the  Feelings.  —  It  may  be  doubted  whether 
the  feelings,  as  such  and  strictly  speaking,  admit  of  classi- 


FEELINGS,    EMOTIONS,    AND   MOVEMENTS.  389 

fication.  We  have  already  shown  that,  in  order  to  be  sub- 
jected to  the  process  of  discrimination  in  self-consciousness, 
feelings  must  actually  have  specific  or  individual  differ- 
ences in  consciousness.  But  in  the  attempt  to  use  these 
differences,  of  which  we  are  conscious,  for  purposes  of 
classification,  we  are  prevented  in  somewhat  the  same  way 
as  that  in  which  we  are  prevented  when  attempting  the 
classification  of  sensations  of  smell.  The  vague,  varied, 
and  shifting  character  of  the  phenomena,  and  their  com- 
plete fusion  with  other  factors  of  the  mental  life,  seem  to 
render  their  scientific  study  exceedingly  difficult. 

It  is  certain  that  no  principle  of  classification  can  be 
suggested  which  undeniably  applies  to  all  the  phenomena 
of  feeling  as  such.  If  we  divide  the  feelings  into  pleas- 
urable and  painful,  we  raise  the  question  whether  there 
are  neutral  or  indifferent  feelings.  And  if  this  question 
is  settled  negatively,  and  the  completeness  of  such  a  two- 
fold division  is  admitted,  the  division  itself  is  of  little 
value,  because  it  does  not  serve  to  describe  the  variations 
among  the  feelings  which  belong  to  either  group  of  the 
two  in  this  "  pleasure-pain  series."  Classifications  resting 
upon  anatomical  and  physiological  differences  are  not,  in 
fact,  classifications  of  the  feelings.  The  same  thing  is  true 
of  all  divisions  suggested  as  arising  out  of  the  relations  in 
which  the  different  feelings  stand  to  the  train  of  ideas. 

Moreover,  the  different  kinds  of  feeling  shade  into  each 
other  by  almost  imperceptible  degrees.  For  example,  the 
sensuous  feelings  cannot  well  be  separated  from  the  sesthet- 
ical,  in  such  cases  as  the  perception  of  the  harmony  of  a 
musical  chord,  or  of  two  adjacent  colored  surfaces.  Even 
the  feelings  which  we  call  moral  are  usually  so  combined 
with  feelings  having  an  obvious  bodily  basis  and  origin  — 
especially  when  the  resulting  states  of  consciousness  attain 
the  strength  of  emotions  —  that  a  strict  separation  of  the 
two  becomes  impossible.  Love,  for  example,  ordinarily 


390  PHYSIOLOGICAL   PSYCHOLOGY. 

involves  elements  of  both  a  more  purely  sensuous  and  a 
more  purely  sesthetical  and  ethical  sort. 

Classes  of  Feelings.  —  It  would  seem  then  that  we  must 
be  content  to  classify  the  feelings,  not  as  such,  but  as  de- 
pendent upon  their  more  prominent  connection  with  other 
classes  of  the  mental  activities.  Even  after  adopting  this 
principle  of  indirect  classification,  we  find  that  the  results 
are  somewhat  indefinite  and  unsatisfactory. 

It  follows  that  neither  the  "physiological"  nor  the  "idea- 
tional "  theory  of  feeling  can  furnish  a  sufficiently  broad 
principle  of  division.  This  statement  is  true  of  Grant 
Allen's  classification  into  (1)  pleasures  and  pains  of  sensa- 
tion and  (2)  so-called  sesthetical  feelings,  —  according  as 
the  activity  of  the  end-organs  in  them  is,  or  is  not,  "  directly 
connected  with  life-serving  function."  It  is  equally  true 
of  the  division,  proposed  by  some  followers  of  Herbart, 
into  (1)  such  feelings  as  are  dependent  upon  the  form  of 
the  course  of  ideas,  and  (2)  such  as  are  conditioned  by  the 
content  of  the  ideas. 

The  following  division  into  four  classes,  according  to 
the  "  natural  organic  variety  "  in  the  activities  of  the  mind 
and  the  characteristic  kinds  and  shades  of  feeling  which 
accompany  them,  is  as  convenient  and  complete  as  any. 
Thus  we  derive  (1)  the  sensuous  feelings,  or  such  as  de- 
pend on  the  different  qualities  of  the  sensations  of  the 
special  senses  and  of  common  feeling ;  (2)  the  cesthetical 
feelings,  or  those  agreeable  and  disagreeable  forms  of  con- 
sciousness which  correspond  to  the  mental  images  of  per- 
ception and  imagination,  regarded  as  beautiful  or  not  (the 
varieties  of  the  feeling  for  beauty  and  its  opposite) ;  (3) 
the  intellectual  feelings,  or  those  which  correspond  to  the 
theoretic  interests  called  out  by  the  higher  forms  of  think- 
ing ;  (4)  the  moral  feelings,  or  those  which  correspond  to 
the  relations  of  desire  and  will. 

The  development  of  the  elementary  feelings  gives  rise 


FEELINGS,    EMOTIONS,   AND  MOVEMENTS.  891 

to  a  great  variety  of  complex  and  mixed  forms.  So-called 
"  higher  feelings,"  or  "  feelings  of  feelings,"  unfold  them- 
selves ;  these  are  dependent  upon  the  complex  relations  of 
society  as  organized  in  its  existing  forms. 

In  general,  the  different  feelings  are  differently  charac- 
terized by  variations  in  content,  rhythm,  strength,  and 
"  tone  "  of  pleasure  or  pain. 

The  Content  of  Feelings.  —  Some  psychologists  have 
denied  that  different  feelings  are  distinguishable  at  all  as 
respects  their  content.  In  other  words,  they  hold  that 
all  feelings  are  to  be  resolved  into  a  mere  quantity  (more 
or  less)  of  pain  or  pleasure;  that  the  "pleasure-pain  series" 
is  the  entire  characteristic  of  feeling,  and  that  different  feel- 
ings have  their  place  in  this  series,  as  different  amounts 
of  the  same  quality  of  mental  states.  .But  such  a  view  is 
plainly  contradictory  of  our  clearest  self-consciousness,  and 
renders  all  scientific  description  of  the  phenomena  of  feeling 
impossible.  It  is  also  virtually  denied  by  all  the  language 
of  feeling.  We  ail  know  that,  and  talk  as  though,  the  feel- 
ing excited — for  example  — by  a  minor  chord  differs  char- 
acteristically from  that  excited  by  a  major ;  the  feeling  of 
a  sensation  of  dark  gray  from  that  of  a  sensation  of  bright 
red ;  of  avarice  from  patriotism ;  of  anger  from  moral  self- 
approbation. 

The  fact  that  those  differences  in  quality  which  the  feel- 
ings undoubtedly  have  are  dependent  upon  differences  in 
the  conditions  of  the  bodily  organism,  or  upon  the  relations 
of  the  ideas  in  the  mental  train,  does  not  abolish,  but  in 
part  explains,  the  characteristic  differences,  in  content,  of 
the  feelings  themselves. 

The  Rhythm  of  Feelings.  —  Like  all  other  mental  phenom- 
ena, the  feelings  occur  in  time-form.  The  movement  in 
the  mental  life  is  marked  by  rhythm  or  periodicity.  This 
movement  is  determined  rhythmically  by  changes  occur- 
ring in  the  conditions  of  the  nervous  system  or  in  the  train 


892  PHYSIOLOGICAL   PSYCHOLOGY. 

of  ideas.  Sometimes  the  feeling  seems  to  pass  back  and 
forth,  by  the  zero-point  in  the  "pleasure-pain  series,"  be- 
tween a  slightly  pronounced  tone  of  pleasure  and  a  slightly 
pronounced  tone  of  pain.  No  very  painful  or  very  pleas- 
ant feelings  are  felt  as  a  steady  tension  of  body  and  mind. 

Strength  of  Feelings.  —  Different  states  of  the  same  kind 
of  feeling,  and  different  kinds  of  feelings,  are  unlike  with 
respect  to  the  amount  of  consciousness  which  they  appro- 
priate or  absorb,  as  it  were.  The  strength  of  feelings 
often  undergoes  a  series  of  rhythmical  changes.  This  is 
one  proof  that  the  condition  of  the  end-organs  and  central 
organs  of  the  nervous  system  determines  the  strength  of 
feeling.  But  the  course  of  the  ideas  is  also  of  influence 
upon  changes  in  strength.  As  the  sensations  or  ideas 
become  more  clear  or  vivid,  the  feelings  attached  to  them 
are  likely  to  increase ;  as  they  become  more  obscure  and 
feeble,  the  attached  feelings  die  away  in  consciousness. 

"  Tone "  of  Feeling,  —  Nearly  all  feelings  are  —  it  is 
admitted  by  all  observers  —  to  be  described  as  either  agree- 
able or  disagreeable.  They  can  therefore  be  arranged,  in 
accordance  with  their  characteristic  agreeable  or  disagree- 
able "tone,"  in  a  so-called  "pleasure-pain  series,"  as  more 
or  less  on  one  side  or  the  other  of  an  indifference-point,  or 
zero-point,  in  the  scale.  Whether  there  exist  states  of 
feeling  that  are  situated  at  this  zero-point  —  and,  there- 
fore, entitled  to  be  called  "  neutral,"  —  has  been  much  dis- 
puted. Neutral  or  indifferent  feelings  were  admitted  by 
Reid,  but  denied  by  Hamilton.  Recently  in  England  a  con- 
troversy has  been  carried  on  between  Bain  and  others  on 
this  subject,  —  the  former  claiming,  and  the  latter  denying, 
that  such  feelings  exist.  Wundt  attempts  to  argue  for 
their  existence  in  a  somewhat  a  priori  manner.  Since  we 
can  plot  the  "  pleasure-pain  series  "  in  a  curve,  part  of 
which  lies  below,  or  on  the  pain-side,  and  part  above,  or  on 
the  pleasure-side,  of  the  neutral  line,  this  curve  must  cross 


FEELINGS,    EMOTIONS,    AND    MOVEMENTS.  393 

the  line  at  some  point  in  its  course.  In  other  words,  it  is 
argued  that  one  cannot  admit  that  painful  feelings  shade 
toward  pleasurable  feelings,  by  less  and  less  degrees  of  pain, 
and  pleasurable  feelings  shade  away  from  the  least  observ- 
ably painful,  by  greater  and  greater  degrees  of  pleasure, 
without  admitting  also  that  neutral  feelings  exist.  The 
reply  to  such  an  argument  is  as  follows :  The  actual  rela- 
tions of  the  qualities  and  quantities  of  states  of  conscious- 
ness cannot  be  accurately  represented  by  the  relations  of 
the  parts  of  material  lines.  The  question,  whether  feel- 
ings exist  which  have  not  the  slightest  tone  of  either  pleas- 
ure or  pain  can  be  answered  only  by  a  direct  appeal  to 
consciousness.  This  appeal  we  believe  results  in  a  nega- 
tive answer. 

Sensuous  Feelings  or  Feelings  of  Sensation.  —  There  are 
some  feelings  which  are  so  connected  and  even  fused  with 
the  sensations  as  to  derive  from  the  latter  their  name. 
According  to  the  physiologist  Strieker,  information  derived 
from  the  peripheral  nerves  consists  of  either  sensations  or 
feelings.  But  both  physiologically  and  psychologically  con- 
sidered the  two  are  different.  In  general,  the  stimulus 
must  affect  the  end-organs  of  sense  in  order  to  give  rise  to 
a  sensation ;  and,  as  we  have  already  seen,  sensations  are 
built  as  factors,  or  elements,  into  the  perceptions  of  exter- 
nal things.  The  physiological  apparatus  of  feeling,  even 
of  the  bodily  sort,  is  probably  to  a  considerable  extent 
different  from  that  of  sensation.  It  is  certain  that  the 
feelings  have  a  peculiar  self-reference,  and  a  characteristic 
tone  of  pleasure  or  pain. 

The  question  has  been  raised  whether  every  sensation 
has  some  feeling,  either  agreeable  or  disagreeable,  con- 
nected or  fused  with  it  in  consciousness.  This  question 
must  be  carefully  distinguished  from  the  question  pre- 
viously raised ;  namely,  as  to  whether  every  feeling 
belongs,  or  not,  in  the  pleasure-pain  series.  We  do  not 


394  PHYSIOLOGICAL   PSYCHOLOGY. 

think  it  accords  with  the  facts  to  declare  that  every  sen- 
sation has  some  feeling.  But  that  multitudes  of  our  sen- 
sations are  characteristically  agreeable  or  disagreeable  does 
not  admit  of  doubt.  In  the  case  of  the  "geometrical 
senses  "  the  feelings  of  pleasure  or  pain,  which  are  fused 
with  the  sensations,  are  localized  as  the  sensations  them- 
selves are  localized.  Indeed,  we  may  speak  of  the  complex 
object  of  self-consciousness  as  a  painful  (or  agreeable)  sen- 
sation, or  as  a  painful  (or  agreeable)  feeling.  The  burning 
coal,  or  the  prick  of  a  needle,  is  described  as  either  a  painful 
sensation,  or  a  painful  feeling,  in  the  finger, — according  as 
we  wish  to  lay  emphasis  on  the  subjective  side  of  the 
suffering,  or  on  the  objective  side  of  the  experience,  as 
bodily  suffering. 

Character  of  "Common  Feeling."  —  At  all  times  in  our 
lives  an  indefinite  variety  of  nervous  impulses  is  pouring  in 
upon  the  cerebral  centres  from  every  part  of  the  periphery 
of  the  body,  and  from  the  lower  parts  of  the  cerebro-spinal 
axis.  Some  of  these  impulses  result  from  changes  in  the 
minute  blood-vessels  and  other  capillaries  about  the  nerve- 
endings  ;  some  from  the  condition  of  the  internal  organs 
and  the  connections  of  the  sympathetic  system  with  the 
cerebro-spinal.  Multitudes  of  impulses  from  all  the  organs 
of  sense,  too  weak  (under  the  existing  conditions  of  the 
cerebral  centres  and  of  mental  occupation)  to  excite  con- 
sciousness, are  constantly  meeting  and  inhibiting  or  rein- 
forcing each  other  in  the  brain.  These  all,  together,  result 
in  a  melange,  or  obscure  mixture,  of  bodily  feelings,  which 
serves  as  a  sort  of  basis  or  background  for  the  more  clearly 
conscious  activities  of  the  mental  life. 

Sensations  in  themselves  heterogeneous  may  be  brought 
into  a  momentary  relation  by  the  partial  identity  of  their 
source  of  excitation,  and  of  the  nervous  connections  within 
the  central  organs.  What  each  of  them  contributes  to  the 
"common  feeling"  depends  upon  this  relation;  it  also 


FEELINGS,   EMOTIONS,   AND  MOVEMENTS.  395 

depends  upon  the  relation  sustained  to  the  mind's  course 
of  ideas,  to  attention,  to  association,  to  habit,  etc.  For 
example,  an  obscure  but  massive  feeling  of  being  ill  at 
ease,  may,  on  our  giving  attention  to  it,  resolve  itself  into 
sensations,  with  painful  feelings  attached,  that  localize 
themselves  in  the  cramped  chest  or  limbs,  the  tired  organs 
of  sense,  the  unhealthy  digestive  apparatus,  etc.  In  con- 
ditions of  ordinary  bodily  health  our  clearly  localized  sen- 
sations, perceptions,  memory-images,  and  thoughts,  are 
always  accompanied  by  an  undercurrent  of  "common 
feeling,"  —  the  "feeling  of  being  in  the  body,"  as  it  is 
sometimes  called. 

JEsthetical  Feelings  in  General.  —  It  has  already  been 
said  that  it  is  difficult  always  to  distinguish  where  the 
sensuous  feelings  end  and  those  feelings  which  we  may 
properly  call  "  sesthetical "  begin.  Characteristic  mixtures 
of  feeling  —  many  of  them  scarcely  to  be  described  —  seem 
to  be  attached  inseparably  to  many  of  our  sensation-com- 
plexes. The  feelings  stirred  by  different  musical  chords 
and  intervals  and  instruments  might  be  instanced  here. 
The  feeling  excited  by  the  same  tune,  as  played  upon  the 
violin  and  then  upon  the  cornet,  is  not  the  same,  irrespec- 
tive of  any  known  influence  from  association.  Goethe 
called  attention  to  the  change  in  spiritual  tone  which 
harmonizes  with  the  sensations  awakened  by  looking 
through  glasses  of  different  colors.  Few  would  deny  that 
sober  feeling  characterizes  sensations  of  black  and  dark 
gray,  excitement  goes  with  red,  cheerfulness  with  light 
green,  sensuousness  with  purple,  cool  quiet  with  dark 
blue,  etc. 

The  distinctively  sesthetical  character  of  the  feeling 
depends,  however,  upon  our  freeing  ourselves  from  recog- 
nition of  the  sensuous  basis.  Pains  and  pleasures  of  the 
skin  and  muscles  and  interior  organs  are  distinctly  unses- 
thetical ;  those  of  smell  and  taste  less  so ;  those  of  hearing 


396  PHYSIOLOGICAL   PSYCHOLOGY. 

and  sight  less  so  still.  Genuinely  sesthetical  feelings  arise 
and  develop  in  connection  with  perception  and  imagina- 
tion ;  they  therefore  imply  an  intellectual  origin  and  law 
of  progress.  They  may  be  said  to  spring  from  the  combi- 
nation of  the  sensuous  feelings  under  the  ideal  forms  of 
space  and  time.  Hearing  is  the  principal  sense  for  the  com- 
bination of  sensuous  feelings  so  as  to  produce  sesthetical 
feelings  under  time-form,  and  sight  (the  "geometrical 
sense  ")  under  space-form. 

jEsthetical  Feelings  of  the  Ear.  —  Harmony  and  rhythm 
are  the  two  principal  forms  of  the  sesthetical  feelings  of 
hearing.  [The  laws  under  which  the  sensation-complexes 
of  consonance  and  dissonance  are  produced,  have  already 
been  discussed  (see  p.  250  f.).]  Harmony  is  colored  by  the 
way  in  which  the  clangs  composing  the  harmony  are  held 
together.  In  the  major  chord  all  the  clangs  are  firmly 
bound  together  by  the  fundamental  clang,  and  a  peculiar 
agreeable  feeling  of  satisfaction  is  the  result.  In  the 
minor  chord  the  coincident  overtone  performs  the  same 
office  less  obviously,  and  the  result  is  an  sesthetical  feeling 
tinged  with  dissatisfaction,  or  longing.  Great  intensity 
of  the  former  kind  of  sensation-complexes  may  involve  the 
pain  of  over-excitement ;  of  the  latter,  the  pain  of  unrest. 

In  musical  time  the  periodicity  of  the  acoustic  sensation- 
complexes,  of  itself,  stirs  the  sesthetical  feelings.  These 
regularly  recurring  impressions,  which  may  have  a  differ- 
ent content  of  sound,  are  combined  into  series;  certain 
members  of  the  series  are  then  accentuated.  Thus  the  two 
fundamental  kinds  of  musical  time,  or  rhythm,  are  origi- 
nated. These  are  "  two-time  "  and  "  three-time  " ;  and  the 
feelings  corresponding  to  each  are  markedly  different.  The 
funeral  march  produces  the  most  pronounced  form  of  the 
sesthetical  feeling  appropriate  to  two-time ;  the  feeling  of 
the  waltz  is  the  typical  form  produced  by  the  musical 
rhythm  of  three-time.  Thus  waves  of  different  forms  of 


FEELINGS,   EMOTIONS,   AND  MOVEMENTS.  397 

gesthetical  feeling  are  made  by  music  to  rise  and  die  away 
within  the  conscious  soul. 

JEsthetical  Feelings  of  the  Eye.  —  The  pleasurable  or  pain- 
ful impressions  which  are  produced  and  fused  with  the 
visual  sensation-complexes,  if  they  are  of  distinctively 
sesthetical  kind,  are  dependent  upon  the  manner  of  the 
combination  of  these  sensation-complexes,  under  the  laws  of 
the  mechanism  of  vision  with  both  eyes  in  motion.  Beau- 
tiful visual  form  is  determined  largely  by  the  course  of  the 
limiting  lines.  These  lines,  in  order  to  arouse  a  pleasura- 
ble sesthetical  feeling,  must  accommodate  themselves  to  the 
laws  of  visual  perception,  as  respects  both  their  direction 
and  their  extent.  Lines  of  slight  curvature,  and  not  too 
far  continued  in  one  direction,  best  comply  with  this 
requirement.  But  lines  of  very  short  curvature,  or  too  far 
prolonged  in  one  direction,  do  not  produce  a  pleasing  ses- 
thetical  effect.  The  mechanism  of  vision  with  both  eyes  in 
motion  favors  lines  lying  chiefly  in  the  horizontal  or  the 
vertical  direction.  Long  oblique  lines  are  scarcely  toler- 
able; since  the  eye  can  sweep  (or  construct)  them  only 
incompletely  and  with  painful  effort. 

The  sesthetical  feeling  for  visual  form  is  also  determined 
by  the  way  in  which  the  form  is  constructed,  through  repe- 
tition and  combination  of  similar  or  dissimilar  shapes.  In 
the  horizontal  direction  the  general  rule  is,  that  we  expect 
symmetry  in  the  arrangement  of  the  simple  parts ;  and 
pleasurable  feeling  arises  at  finding  our  expectation  met. 
In  the  vertical  direction,  however,  asymmetry  is  the  right 
rule.  These  rules  are  dependent,  in  part,  on  our  habit, 
and  upon  the  consequent  ease  with  which  we  master  the 
details  of  a  complex  field  of  visual  perception.  Certain 
proportions  between  the  whole  and  the  parts,  and  between 
the  connected  parts  of  the  whole,  are  favorable  to  the  de- 
velopment of  pleasurable  sesthetical  feeling.  The  so-called 
"  golden  diameter "  —  or  rule,  that  the  whole  of  a  visual 


398  PHYSIOLOGICAL  PSYCHOLOGY. 

perception  shall  be  to  the  larger  part  as  the  larger  part  is 
to  the  smaller  part  (x  +  1 :  x : :  x  :  1)  —  is  claimed  by  some 
writers  to  hold  true. 

Intellectual  Feelings.  —  It  has  already  been  seen  that 
intellectual  elements  blend  more  and  more  with  the  causes 
which  determine  the  character  of  our  feelings,  as  we  pass 
from  the  lower  and  more  obviously  sensuous-  to  the  higher 
and  more  distinctively  sesthetical.  The  various  activities 
of  the  mind,  called  intellectual,  have  their  peculiar  forms  of 
pleasurable  or  painful  feeling  connected  with  them.  As 
to  the  physical  basis  of  these  feelings  we  are  much  in  the 
dark.  It  is  obvious,  however,  that  feeling  is  connected,  in 
general,  with  all  mental  action.  Pleasurable  feeling  arises 
where  the  time-rate  of  the  ideas  is  moderate,  and  the  move- 
ment of  the  mental  train  is  accompanied  by  no  severe 
demands  upon  the  attention ;  painful  feeling,  where  the 
time-rate  is  too  slow  or  too  hurried,  and  the  movement  of 
the  mental  train  "  tasks  "  (as  we  say)  the  powers  of  volun- 
tary attention. 

The  more  immediate  dependence  of  the  feelings  on  the 
relations  of  the  ideas  composing  the  mental  train  is  a  subject 
which  has  been  treated  with  great  skill  and  insight  by 
those  psychologists  whose  view  was  previously  mentioned 
(see  p.  385  f.).  The  discussion  of  this  view  —  the  view  of 
Herbart  and  his  followers  —  does  not  fall  within  the  prov- 
ince of  physiological  psychology.  What  is  called  the 
"inhibition"  and  the  "furtherance  "  of  one  idea  by  another 
doubtless  has  its  physiological  basis.  This  basis  is  con- 
trolled by  the  same  laws  of  exhaustion  and  renewal  of  the 
nervous  elements,  and  of  the  reciprocal  dependence  in 
which  these  elements  stand  toward  each  other,  which  we 
have  seen  to  hold  good  for  the  entire  nervous  system. 
Indeed,  all  such  laws  have  their  highest  and  fullest  exem- 
plification in  the  case  of  the  cerebral  centres.  When,  for 
example,  we  are  painfully  trying  to  recall  a  forgotten 


FEELINGS,   EMOTIONS,   AND  MOVEMENTS.  399 

name  or  date,  what  the  Herbartian  theory  refers  to  as 
an  "  inhibition  "  of  ideas,  is  perhaps,  physiologically  con- 
sidered, a  physical  conflict  between  several  inchoate  molec- 
ular processes  that  are  trying  to  master,  as  it  were,  a 
particular  region  of  the  brain.  But  science  is  as  yet 
unable  to  work  out  these  laws  in  detail. 

Influence  of  Association.  —  From  the  point  of  view  of  con- 
sciousness, the  influence  of  association  over  the  character 
of  our  feelings  is  almost  too  well  known  to  require  remark. 
What  physiological  psychology  can  say  as  to  the  explana- 
tion of  the  association  of  ideas,  in  general,  will  be  referred 
to  elsewhere.  It  is  enough  at  present  to  remark,  that  all 
kinds  of  feelings  —  sensuous,  sesthetical,  and  intellectual  — 
come,  of  course,  under  the  principle  of  association.  In 
this  way  all  the  more  complex  peculiarities  of  individuals, 
epochs,  nationalities,  etc.,  are  best  accounted  for.  The 
sesthetical  feelings  of  the  Highlander  when  he  hears  a  bag- 
pipe, of  the  citizen  of  the  United  States  when  he  perceives 
a  certain  arrangement  of  red  and  blue  colors  on  a  back- 
ground of  white,  of  the  Englishman  when  he  hears  the 
words  "Her  majesty,"  etc.,  all  belong  under  this  principle. 
Under  the  action  of  this  principle,  "  feelings  of  feelings," 
the  complex  sentiments,  and  mental  moods,  are  constituted. 
If  we  introduce  the  principle  of  heredity,  and  consider  the 
whole  subject  from  the  evolutionary  point  of  view,  we 
shall  doubtless  conclude  that  many  forms  of  feeling  which 
now  seem  most  primary  and  instinctive  have  really  been 
acquired,  under  the  laws  of  association  and  habit,  in  the 
developing  life  of  the  race.  But  all  this  would  carry  us 
too  far  from  our  somewhat  restricted  field. 

THE  EMOTIONS  AND  BODILY  MOVEMENTS. 

All  the  feelings,  when  their  intensity  as  states  of  con- 
sciousness is  greatly  increased,  are  accompanied  by  marked 
changes  in  the  condition  and  action  of  the  bodily  organs. 


400  PHYSIOLOGICAL  PSYCHOLOGY. 

These  changes  in  the  bodily  basis  of  the  feelings  react 
upon  the  character  of  the  feelings  themselves,  and  modify 
them  most  profoundly.  Moreover,  there  are  some  kinds 
of  feeling,  whose  characteristics  are  chiefly  determined, 
in  whatever  degree  they  are  manifested,  by  the  condition 
and  action  of  the  bodily  organs.  "  Affections  "  and  "  Emo- 
tions" so-called  are  developed  from  all  forms  of  feeling 
when  intensified  to  a  sufficient  degree.  "Passions"  are 
those  states  of  feeling  in  which  the  very  character  of  the 
feeling  itself  may  be  most  appropriately  described  as  the 
feeling  of  a  deranged  and  over-excited  bodily  organism. 

Characteristics  of  the  Affections,  Emotions,  and  Passions,  — 
The  consideration  of  all  affectional  or  emotional  forms  of 
feeling  involves  these  three  important  particulars :  (1)  The 
characteristic  feeling  which  distinguishes  each  from  the 
others;  (2)  the  relation  of  the  feeling  to  the  chain  of 
ideas,  and  the  changes  induced  by  the  feeling  in  the  move- 
ment of  the  ideas ;  and,  especially,  (3)  its  relations  to  the 
different  bodily  organs,  and  the  reflex  effect  of  the  changes 
in  these  organs,  both  directly  upon  the  feeling  itself,  and 
indirectly  upon  the  feeling  through  the  disturbance  of  the 
ideas. 

All  affections  and  passions  may  be  considered,  psycho- 
logically, as  having  their  rise  in  some  form  of  blind,  in- 
stinctive impulse.  Impulse  becomes  connected,  in  the 
development  of  experience,  with  perceptions  and  mental 
images  of  the  objects  that  have  excited  or  satisfied  it. 
When  this  connection  is  established  between  the  feeling, 
which  as  blind  impulse  takes  no  intellectual  account  of 
the  object,  and  appropriate  perceptions  or  mental  images, 
the  basis  for  an  affection  or  emotion  is  laid. 

Instinctive  impulses  are  of  two  general  classes,  —  those 
of  attraction  or  craving,  and  those  of  repulsion.  The 
natural  germ  of  anger  or  hate,  for  example,  is  found  in 
that  blind,  instinctive  impulse  of  resistance,  with  its  accom- 


FEELINGS,    EMOTIONS,    AND   MOVEMENTS.  401 

panying  feeling  of  painful  irritation,  which  all  sudden  and 
intense  excitements  of  the  nervous  system  arouse.  In  the 
child,  or  childish  adult,  anger  bursts  out  against  the  inani- 
mate object  which  causes  pain  or  opposes  freedom  of  move- 
ment. On  the  other  hand,  the  affection  of  the  child  is 
nursed  by  the  feeling  of  comfort  it  has  in  the  arms,  or  at 
the  breast,  of  the  mother.  By  a  growing  variety  of  experi- 
ences, the  impulses  of  attraction  or  repulsion  become  diver- 
sified into  a  number  of  affections  and  passions,  characteristic 
of  the  different  manifold  relations  in  which  the  mind  stands 
toward  things  and  persons. 

All  emotional  forms  of  feeling  are  characterized  by 
abrupt  and  sudden  changes  in  the  character  and  time- 
course  of  the  train  of  ideas.  Any  sudden,  strong  stimulus 
—  as  we  all  know  —  breaks  in  upon  and  destroys  the  steady 
and  peaceful  flow  of  mental  life.  It  has  sometimes  been 
said  that  from  feeling  to  emotion  is  a  "leap."  The  ten- 
dency of  any  violent  change  of  mental  state  is,  then,  to 
excite  an  "  emotional "  condition  of  the  feelings,  character- 
ized by  the  peculiar  kind  of  feeling  which  is  appropriate 
to  the  particular  character  of  the  object  or  mental  image 
which  absorbs  the  state.  All  the  emotions  take  men  "  off 
their  guard."  They  "upset,"  "banish,"  "interrupt,"  the 
train  of  ideation.  The  members  of  this  train,  thus  dis- 
turbed by  the  springing  in  upon  them  of  emotion,  become 
hurried,  disordered,  crowded,  confused. 

But,  on  the  other  hand,  the  effect  of  so  marked  and 
rapid  a  disturbance  of  the  mental  train  reacts  upon  the 
emotion  itself.  The  mind  feels  the  disturbance  of  the  ideas 
as  a  new  emotion,  or  as  an  added  characteristic  of  the 
former  kind  of  emotion.  The  stream  of  conscious  ideation 
being  perturbed,  the  feeling  of  the  perturbance  is  an  emo- 
tional condition  of  the  entire  conscious  life.  Without 
doubt  this  mental  confusion  is  indicative  of  an  unusual 
molecular  agitation,  of  a  derangement  of  the  circulation 


402  PHYSIOLOGICAL   PSYCHOLOGY. 

and  psycho-physical  chemistry,  in  the  ideo  and  sensory- 
motor  centres  of  the  cerebral  hemispheres.  But  here  again 
we  know  little  or  nothing  of  the  particulars. 

It  is  the  remarkable  and  characteristic  effect  which  such 
forms  of  feeling  produce  upon  certain  particular  organs, 
that  is  the  most  noteworthy  peculiarity  of  all  affections, 
emotions,  and  passions.  The  influence  of  shame,  fear,  or 
anger,  upon  the  vaso-motor  system  and  the  circulation  of 
the  blood,  is  well-known.  But  some  persons  grow  pale, 
and  some  red,  when  angry.  In  experiment  upon  the  lower 
animals,  the  curve  which  indicates  the  amount  of  blood- 
pressure  is  altered  by  the  cerebral  disturbance  attending 
emotions  of  surprise,  fear,  or  other  similar  excitement. 
Care,  anxiety,  strong  love  or  hate,  and  all  the  passions, 
produce  changes  in  the  action  of  the  capillary  vessels, 
upon  the  secretions,  the  nutrition,  etc. 

The  effect  of  some  of  these  forms  of  feeling  is  chiefly  to 
depress,  and  of  others  chiefly  to  over-excite,  the  action 
of  the  vital  organs.  Hence  the  division  which  Kant  made 
of  the  affections,  into  "sthenic"  or  "asthenic."  The 
former  lame  or  kill  by  apoplexy,  the  latter  may  kill  by 
laming  the  heart. 

But  this  characteristic  effect  of  the  affections,  emotions, 
and  passions,  upon  the  internal  and  vital  organs  of  the  body, 
reacts  upon  the  feelings  themselves.  Of  this  effect,  anger 
is  a  notable  example.  Under  the  influence  of  this  pas- 
sion, the  teeth  are  set,  the  fists  are  clenched,  the  heart- 
beats quicken,  the  breathing  becomes  shallow,  the  limbs 
are  stiffened  or  made  to  tremble,  the  organs  of  the  abdo- 
men are  stirred,  the  creeping  sensations  of  "  goose-flesh  " 
occur,  the  nostrils  dilate.  This  mingling  of  sensations, 
with  their  characteristic  feelings,  and  of  so-called  common 
feeling,  forms  the  physical  basis,  as  it  were,  of  a  rising 
tide  of  emotion.  The  tide  subsides,  of  necessity,  as  the 
nervous  exhaustion  caused  by  over-excitement  of  the 


FEELINGS,   EMOTIONS,   AND   MOVEMENTS.  403 

organism  comes  on.  Indeed,  the  control  of  the  passion 
may  be  indirectly  undertaken  by  keeping  down  the  influ- 
ence of  these  sensuous  feelings.  Who  can  continue  his 
rage,  —  with  limp  muscles,  deliberate  and  regular  breath- 
ing, relaxed  jaws  and  fists,  and  a  placid  face  ? 

It  has  already  been  shown  that  even  the  feelings  called 
sesthetical  or  intellectual — and,  we  might  add,  ethical  and 
religious  —  when  they  are  aroused  by  mental  images  to  a 
high  degree  of  intensity,  tend  to  assume  an  emotional  char- 
acter. They  then  partake  of  all  the  qualities  which  have 
just  been  described. 

The  Mental  Moods.  —  Few  things  are  more  well-estab- 
lished in  the  popular  estimate  than  the  existence  of 
so-called  "  moods  "  of  the  mind.  By  so  vague  a  term  we 
designate  certain  general  differences  in  the  average  char- 
acter of  the  complex  states  of  feeling  by  which  individuals 
are  characterized.  By  the  same  term  we  also  designate 
similar  differences  which  characterize  different  periods, 
longer  or  shorter,  in  the  life  of  the  same  individual. 

We  have  spoken  of  the  "mood"  as  a  characteristic 
complex  of  feelings.  This  is  because  the  influence  of  the 
sensations,  perceptions^  and  train  of  ideas,  upon  the  gen- 
eral "  tone "  of  the  mental  life  is  to  be  considered  as 
expressing  itself  in  the  mixture  of  feelings.  The  principal 
elements  that  determine  any  particular  "  mood  "  consist  of 
ill-localized  sensations  arising  from  the  visceral  organs,  accel- 
erated or  disturbed  and  depressed  cerebral  functions  con- 
nected with  the  reproduction  of  the  ideas,  vague  single 
feelings  of  the  suppressed  emotional,  or  the  sesthetical  or 
intellectual  or  ethical,  type,  etc.  The  passions  and  emo- 
tions, distinctly  as  such,  run  their  course  quickly,  and  give 
color  to  the  personality  chiefly  by  the  frequency  of  their 
recurrence  and  the  vehemence  of  their  force  while  they 
last.  But  mental  moods  are  slower  in  change  and  less 
strong  in  tone ;  they  are  characterized  by  affections  and 


404  PHYSIOLOGICAL   PSYCHOLOGY. 

emotions  of  a  low  and  lingering  character,  —  pale  and 
faded  specimens  of  the  type,  as  it  were.  • 

It  will  appear  that  mental  "  moods  "  —  as  respects  their 
endurance  in  time,  their  complexity  (quality  of  being  mix- 
tures of  a  vast  number  of  obscure  elements),  and  their 
dependence  upon  the  constitution  and  functions  of  the 
entire  bodily  mechanism  —  stand  midway  between  "tem- 
peraments" and  the  particular  complex  states  of  feeling 
which  characterize  our  changing  daily  experience. 

Another  class  of  mental  states,  whose  existence  and 
nature  are  intimately  connected  with  the  direction  of  the 
bodily  movements,  consist  of  the  so-called  — 

Feelings  of  Effort,  or  of  Innervation.  —  The  testimony  of 
universal  experience  is  perfectly  clear  to  the  fact  that  we 
know  —  it  would  be  said  by  most  persons,  instinctively 
and  immediately  —  the  position  and  condition,  as  respects 
tension  and  strain,  of  our  bodies  and  their  individual  mem- 
bers. But  we  have  already  seen  (p.  316  f .)  that  this  knowl- 
edge is  the  result  of  a  development.  It  is  of  the  nature  of 
perception ;  and  it  is  dependent  upon  a  variety  of  localized 
sensation-complexes  arising  from  the  stimulation  of  skin, 
muscles,  tendons,  and  joints.  [Among  these,  the  amount 
of  influence  exerted  by  the  "muscular  sensations"  has 
been  much  disputed.  It  is  not  necessary,  however,  in  this 
connection  to  repeat  the  arguments  which  have  led  us  to 
assign  to  them  a  principal  part,  but  not  the  whole,  of  the 
influence  in  constructing  our  perceptions  of  the  bodily 
positions,  strains,  and  movements.] 

It  is  plain  that  the  view  previously  taken  assigns  a 
peripheral  origin  to  the  so-called  "  feelings  of  effort."  But 
the  question  arises  whether  their  origin  is  wholly  periph- 
eral ;  whether,  in  fact,  it  is  not  partly,  at  least,  of  a  central 
origin.  The  great  physiologist  Miiller  considered  the  ner- 
vous process  which  occasions  the  "  feeling  of  effort "  to  be 
of  purely  central  origin,  and  to  consist  of  a  discharge  from 


FEELINGS,    EMOTIONS,   AMD   MOVEMENTS.  405 

the  motor  centre  into  the  motor  nerves.  In  other  words, 
it  is  the  feeling  of  the  cerebral  process  which  innervates  the 
group  of  muscles,  on  occasion  of  a  fiat  of  will.  Wundt 
takes  the  same  view,  and  regards  this  class  of  feelings, 
(which,  in  his  opinion,  differ  only  as  respects  quantity  and 
not  as  respects  quality,)  as  of  chief  importance  in  account- 
ing for  our  experience  of  solid  objects  of  sense  and  of 
whatever  belongs  to  the  inertia  of  matter  in  general. 

The  question,  whether  any  elements  of  the  compound 
"  feeling  of  effort "  are  directly  dependent  upon  the  cere- 
bral changes  which  immediately  accompany  an  act  of  will, 
cannot  be  said  to  be  experimentally  settled.  On  the  whole, 
however,  the  tendency  is  in  our  judgment  to  discredit  the 
alleged  proofs  of  such  a  central  origin  to  this  feeling.  For 
it  seems  possible  to  account  for  most,  if  not  all,  of  our 
experience  of  the  different  forms  of  "  the  feeling  of  effort," 
on  the  theory  of  the  peripheral  origin  of  the  factors  which 
compose  it.  For  example,  it  has  been  claimed  that,  if  we 
intensely  make-believe  to  use  any  limb  (let  it  be  in  pulling 
with  the  finger  the  imaginary  trigger  of  a  gun),  but  do 
not  actually  move  it,  we  nevertheless  have  the  conscious- 
ness of  exerting  effort.  In  reply  it  has  been  pointed  out, 
that  the  feeling  of  effort  in  such  cases  is  due  to  keeping 
the  glottis  tightly  closed,  while  actively  contracting  the 
respiratory  muscles.  Let  all  these  parts  be  carefully  kept 
relaxed,  and  we  cannot  even  imagine  ourselves  to  be 
"  making  the  effort "  of  using  the  limb. 

It  is  further  alleged,  in  evidence  of  the  central  origin 
of  the  feeling  of  effort,  that  persons  afflicted  with  cortical 
paralysis  can  produce  the  consciousness  of  stress  of  will  in 
the  imaginary  movement  of  the  paralyzed  limb.  But  in 
such  a  case  this  feeling  is  probably  due  to  the  condition 
of  the  joints  and  muscles.  Even  where  the  limb  is  wholly 
lamed,  the  feeling  is  actually  produced,  as  a  rule  at  least, 
by  a  movement  or  condition  of  squeezing  and  straining, 


406  PHYSIOLOGICAL   PSYCHOLOGY. 

produced  in  some  sound  but  closely  allied  part  of  the  body. 
Thus  Vulpian  noticed  that  his  patients  produced  the  feeling 
of  effort  in  the  lamed  fist  by  actually  closing  the  sound  one. 
Another  observer  (Miinsterberg)  can  allege  no  little  ex- 
perimental evidence,  when  he  contends  that  involuntary 
contraction  of  the  muscles  of  sight,  tension  of  the  scalp, 
etc.,  may  be  translated  into  the  exertion  of  energy  localized 
in  different  and  distant  parts  of  the  body. 

The  case  of  the  eye,  when  afflicted  with  partial  paralysis 
of  the  external  rectus,  is  almost  classical.  Patients  having 
this  form  of  paralysis  localize  the  visual  object  too  far  out, 
on  the  side  of  the  lamed  eye.  The  argument  is  as  follows : 
The  patient  feels  that  he  has  moved  his  eye  much  farther 
than  he  really  has;  he  therefore  localizes  the  object  by 
this  exaggerated  feeling  of  effort.  Since  the  peripheral 
result  actually  accomplished  is  a  diminished  effort,  the 
feeling  of  the  effort  cannot  originate  from  this  result,  but 
must  have  a  central  origin.  In  reply  to  this  argument  it 
has  been  pointed  out  (especially  by  Professor  James)  that 
the  argument  entirely  neglects  what  goes  on  in  the  other 
and  sound  eye.  The  sound  eye,  unlike  the  lame  one,  con- 
tinues its  motion  until  the  normal  limit  is  reached,  and 
the  corresponding  amount  of  peripheral  strain  produced. 
Since  the  two  eyes  operate  as  one  instrument,  the  object 
is  necessarily  localized  by  the  condition  of  the  sound  eye, 
no  less  than  the  lamed  eye. 

Testimony  from  persons  who  have  suffered  the  amputa- 
tion of  limbs  is  ambiguous.  A  considerable  proportion  of 
such  persons  (perhaps  about  three  quarters)  report  that 
they  have  had,  for  a  longer  or  shorter  time  subsequent  to 
the  amputation,  the  feelings  of  position,  strain,  and  move- 
ment, in  the  lost  limb.  The  majority  of  those  who  have 
lost  a  leg  or  arm  have  the  feeling  in  the  foot  or  hand ;  but 
feel  the  parts  intervening  between  these  members  and  the 
stump,  less  vividly  or  not  at  all.  Many  who  have  lost  a 


FEELINGS,    EMOTIONS,   AND   MOVEMENTS.  407 

leg  can  "  work  "  or  "  wriggle  "  their  toes  at  will,  —  feeling 
both  the  effort  and  the  movement ;  but  in  most  cases  actual 
movements  in  the  muscles  of  the  stump  can  be  detected.  It  is 
probable  that  where  such  movements  cannot  be  detected, 
the  feeling  of  effort  originates  in  the  strain,  or  movement 
of  other  peripheral  parts. 

The  connection  of  this  discussion  with  a  theory  of  the 
will,  and  with  the  dependence  of  acts  of  will  upon  a  bodily 
basis,  is  obvious.  The  nature  of  the  connection  will  be 
referred  to  in  another  place.  It  is  pertinent  here  to  con- 
clude that,  excluding  what  is  purely  "  moral "  (the  choice 
and  what  is  psychologically  involved  in  it),  the  so-called 
"  feeling  of  effort "  is  probably  of  peripheral  origin.  In  fact, 
it  should  not  be  called  a  feeling  at  all.  It  is  rather  a  mix- 
ture of  sensation-complexes  arising  from  the  condition  of 
the  skin,  muscles,  tendons,  and  joints,  and  becoming  local- 
ized (often  in  a  very  imperfect  and  illusory  way)  under 
the  influence  of  the  stronger  factors  in  the  perception,  and 
in  connection  with  the  associated  mental  images  and  the 
accompanying  "  fiat  of  will." 

How  easily  the  true  character  of  a  complex  perceptive 
process  can  be  misapprehended  by  the  conscious  mind, 
when  this  process  is  dependent  upon  a  mixture  of  obscure 
and  indefinite  sensations,  is  made  apparent  by  facts  like 
the  following.  A  certain  patient,  who  had  complete 
ansesthesia  and  was  wholly  unable  to  discover  unseen  active 
or  passive  movements  of  his  own  body,  could  put  forth  the 
amount  of  effort  to  raise  a  given  weight,  in  case  he  under- 
stood ly  sight  its  nature  and  its  size.  Otherwise  he  could 
not  even  approximately  estimate  or  control  the  amount  of 
muscular  contraction  necessary.  It  would  appear,  then, 
that  in  this  patient's  case,  the  requisite  "  fiat  of  will "  was 
estimated  and  controlled  by  memory-images  of  sight  with- 
out help  from  the  so-called  "  feeling  of  effort." 

Kinds  of  Bodily  Movements.  —  Changes  of  the  position  of 


408  PHYSIOLOGICAL  PSYCHOLOGY. 

our  bodies  and  their  members,  considered  in  relation  to 
the  conscious  mental  processes,  are  of  two  kinds.  These 
are  (1)  movements  not  dependent  upon  states  of  con- 
sciousness, and  (2)  movements  that,  for  their  explanation, 
require  us  to  take  account  of  antecedent  states  of  con- 
sciousness. Of  the  former,  again,  two  subdivisions  may 
be  made,  —  the  automatic  and  the  reflex.  The  nature  and 
origin  of  both  these  forms  of  bodily  movement  have 
already  been  sufficiently  discussed  (Chapter  VI.). 

It  should  be  noticed  in  this  connection  that  sensations, 
ideas,  and  acts  of  will,  which  have  to  do  with  the  move- 
ments of  the  body,  constantly  tend,  as  it  were,  in  two 
directions,  —  either  toward  consciousness  or  out  of  it. 
The  physical  correlate  of  this  statement  is  doubtless  as 
follows :  The  nervous  processes  which  stimulate  to  motion 
the  different  groups  of  muscles,  rise  and  fall,  with  varying 
degrees  of  intensity,  toward  and  away  from  the  higher 
cerebral  centres. 

In  the  case  of  reflex  movements,  unaccompanied  by 
those  changes  in  consciousness  that  are  called  ideo-motor 
or  voluntary-motor,  either  the  "arc,"  around  which  the 
neural  processes  are  completed,  has  its  highest  point  below 
the  cerebral  hemispheres ;  or  else  the  processes  which  rise 
into  these  hemispheres  are  .relatively  too  weak  to  produce 
any  sufficient  effect  within  the  centres  concerned  in  such 
ideo-motor  and  voluntary-motor  control  of  the  muscles. 
In  the  case  of  unconscious  automatic  motion,  the  cerebral 
excitations  which  originate  centrally  —  in  changes  of  the 
blood-supply,  etc.  —  do  not  involve,  at  least  with  sufficient 
intensity,  these  ideo-motor  and  voluntary-motor  centres. 

It  is  by  means  of  these  processes,  in  the  two  directions 
just  described,  that  our  learning  and  practice  of  all  com- 
plicated movements  of  the  body  takes  place.  Such  move- 
ments are  those  concerned  in  feats  of  dexterity  and  skill, 


FEELINGS,    EMOTIONS,    AND    MOVEMENTS.  409 

in  learning  to  handle  tools,  to  play  on  musical  instruments, 
etc. 

Impulsive  Movements.  —  Those  changes  of  the  position 
of  the  body  and  its  members  which  involve  states  of  con- 
sciousness may  be  divided  into  the  impulsive  and  the  vol- 
untary. This  distinction  requires,  however,  such  a  variety 
of  degrees  that  shade  into  each  other  as  to  be  difficult  of 
application.  By  an  impulsive  movement  we  understand 
one  which,  without  a  conscious  fiat  of  will,  follows  upon 
certain  states  of  ideation  and  of  excited  feeling.  The 
motif  for  such  a  movement  may  be  said  to  lie  in  the  "  im- 
pulse," or  push,  of  feeling,  which  determines  volition  one 
way,  without  any  proper  choice. 

Impulsive  movements  form  the  basis  of  the  more  dis- 
tinctively voluntary.  They  are  particularly  prominent 
and  influential  in  the  early  development  of  the  mind. 
The  neural  processes,  awakened  in  the  brain  of  the  infant 
by  the  action  of  various  forms  of  stimulus  upon  the  end- 
organs  of  sense,  are  themselves  the  stimuli,  or  awakeners, 
of  states  of  consciousness.  The  tone  of  these  states  of  con- 
sciousness is  one  of  either  pleasure  or  discomfort.  By  the 
natural  mechanism  of  the  body,  certain  forms  of  move- 
ment are  connected  with  these  states  of  feeling,  which  in 
general  tend  to  enhance  the  feeling,  if  pleasurable,  and  to 
relieve  it,  if  unpleasant.  Thus  certain  bodily  movements 
become  connected  with  certain  states  of  conscious  feeling. 
More  indirectly,  the  same  movements  become  connected 
with  the  ideas  and  perceptions  associated  with  the  feelings. 
The  reaction-time  is  shorter  for  the  impulsive  movements 
than  for  the  voluntary ;  since  "  will-time "  proper  is 
dropped  out  (see  p.  371  f.). 

It  is  obvious,  that  the  line  between  the  automatic  and 
the  impulsive  movements,  in  the  earliest  life  of  the  child, 
cannot  be  drawn  with  confidence.  And,  inasmuch  as  the 
same  thing  is  true  of  the  automatic  and  the  reflex  move- 


410  PHYSIOLOGICAL  PSYCHOLOGY. 

ments,  all  three  of  these  classes  (reflex,  automatic,  and 
impulsive)  are  closely  allied.  It  is  impossible  to  say  how 
much  of  the  almost  constant  movement  of  an  infant's  limbs 
is  reflex,  how  much  automatic.  It  is  equally  impossible  to 
decide,  in  all  individual  cases,  between  the  reflex  and  the 
impulsive  explanations  of  the  grimaces  of  its  face,  its 
starting  at  sounds,  etc.  There  is  no  doubt  that  the  gen- 
eral order  of  development,  however,  is  from  the  reflex  and 
automatic  to  the  impulsive. 

Voluntary  Movements.  —  Those  changes  of  position  in 
the  body  and  its  members,  which  are  ordinarily  called 
" voluntary"  are  so  in  reality  only  with  respect  to  some 
of  their  elements.  They  involve  other  elements  which 
are  reflex,  centrally  co-ordinated,  and  impulsive.  Nor  must 
we  understand  "  voluntary,"  in  this  connection,  necessarily 
to  imply  conscious  deliberation  and  choice,  —  an  "act  of 
free-will  "  in  the  fullest  meaning  of  the  words. 

Voluntary  movements  are  the  highest  class  of  move- 
ments, from  the  psycho-physical  point  of  view,  because 
they  require  for  their  completion  the  entire  psycho-physi- 
cal mechanism.  They  imply  a  development  of  both  bodily 
and  mental  powers.  They  involve  the  five  following  con- 
ditions :  (1)  The  possession  of  an  educated  reflex-motor 
mechanism,  under  the  control  of  those  centres  of  the  brain 
that  are  connected  with  the  phenomena  of  consciousness ; 
(2)  impulses,  in  the  form  of  conscious  feelings  that  have 
a  tone  of  pleasure  or  pain  and  have  become  associated 
with,  (3)  mental  images  of  movements  and  positions  of  the 
bodily  members  that  experience  has  taught  us  are  them- 
selves connected  with  these  pleasurable  or  painful  states 
of  feeling ;  (4)  a  conscious  fiat  of  will,  or  order,  as  it  were, 
for  the  realization  of  these  mental  images ;  and  (5)  a  cen- 
tral nervous  mechanism  in  which,  as  a  matter  of  natural 
or  acquired  causation,  the  requisite  motor  impulses  may 


FEELINGS,   EMOTIONS,    AND   MOVEMENTS.  411 

arise,  to  go  forth  along  their  nerve-tracts  to  the  groups  of 
muscles  concerned. 

Careful  study  of  these  five  groups  of  very  complex  con- 
ditions, both  of  nervous  system  and  states  of  conscious 
mind,  convinces  us  that  the  science  of  physiological  psy- 
chology can  deal  in  only  a  very  fragmentary  and  doubtful 
way  with  most  of  the  problems  involved.  Of  the  first, 
second,  and  fifth  groups  (Nos.  (1),  (2),  and  (5))  enough 
has  already  been  said.  Of  the  possibility  of  a  psycho- 
physical  theory  of  the  "fiat  of  will"  (No.  4),  as  connected 
with  choice,  control  of  attention,  freedom,  etc.,  we  shall 
speak  more  at  length  in  another  place.  A  few  remarks 
may  here  be  made  concerning  the  "  ideo-motor  "  character  of 
this  class  of  bodily  changes  (No.  3). 

To  will  the  movement  of  any  particular  group  of  mus- 
cles we  must  have  had  experience  of  the  actual  movement 
of  that  group ;  i.e.  of  the  changes  in  the  feeling  of  effort, 
in  the  perceptions  and  constitution  of  the  entire  mental 
life,  which  such  particular  movement  involves.  We  can 
never  "  will "  motion  in  general  —  motion,  that  is,  of  no 
particular  member  of  the  body,  and  without  specific  qual- 
ity, direction,  and  velocity  of  motion.  Each  member,  and 
each  position  of  each  member,  and  each  kind,  direction, 
and  velocity  of  movement,  has  its  own  mental  representa- 
tives in  the  ideation-processes  of  the  mind.  It  is  by  these 
mental  images  that  the  particular  "fiat  of  will"  guides 
itself  in  each  case.  We  can  issue  the  requisite  fiat  of  will 
by  attention  (whether  forced  or  voluntary)  to  the  appro- 
priate ideo-motor  images ;  but  in  no  other  way.  Otherwise, 
the  distinction  between  impulsive  and  voluntary  move- 
ments is  lost,  and  there  is  no  accounting  for  the  particular 
character  of  the  movement  which  takes  place. 

Dependence  of  Perception  on  Movement.  —  Perception  is 
a  knowledge  of  "  Things  "  ;  and  all  things  are  known  to  us 
as  being  external  and  having  extension  in  space.  Indeed, 


412  PHYSIOLOGICAL   PSYCHOLOGY. 

this  is  as  true  of  our  bodily  members  as  it  is  of  the  remoter 
objects  which  we  learn  to  know  through  them.  Now  it  is 
this  life  of  motion  which  gives  reality  to  all  things,  whether 
they  are  regarded  as  parts  of  our  bodies  or  are  known  as 
separable  from  our  bodies.  Were  it  not  that  the  child  is, 
from  the  beginning  of  its  life,  excited  to  movements  — 
reflex,  automatic,  and  impulsive  —  and  so  acquires  an  ex- 
perience of  feelings  of  effort  and  of  mental  images  repre- 
sentative of  all  manner  of  movements,  it  could  never  gain 
a  knowledge  of  a  real  world  of  things. 

So  true  is  this  that  we  cannot  even  form  the  vivid  men- 
tal image  of  anything,  or  of  any  change  in  the  shape  or 
position  of  anything,  without  evoking  inchoate  movements 
to  serve,  by  the  sensation-complexes  which  they  occasion, 
as  factors  in  our  mental  image.  In  the  effort  to  form  such 
an  image  of  a  chair  or  a  table,  for  example,  we  institute  a 
series  of  extremely  subtle  and  delicate  motor  impulses  of 
the  eye  or  the  hand,  —  of  the  senses  with  which  we  realize 
it.  The  effort  to  image  a  solid  object  revives  the  appropriate 
inchoate  motor  impulses  that  are  wont  to  control  the  active 
perception  of  that  object. 

The  Expressive  Movements.  —  A  certain  appropriateness, 
or  naturalness  of  connection,  is  recognized  by  every  one  as 
existing  between  some  classes  of  ideas  and  feelings  and 
those  positions  and  movements  of  the  body  which  express 
them.  In  this  field  comparative  psychology  and  anthro- 
pology are  particularly  successful. 

In  explaining  this  class  of  movements  Wundt  has  sum- 
marized the  phenomena  under  the  following  three  prin- 
ciples :  —  (1)  the  principle  of  the  direct  alteration  of 
innervation.  Strong  emotions,  with  vivid  ideas,  exercise 
an  immediate  reaction  on  certain  cerebral  centres.  This 
results  in  exciting  some  groups  to  action  or  increased  ten- 
sion ;  and  other  groups  of  muscles  are  lamed  by  the  same 
process  of  central  innervation.  Hence  the  trembling  of 


FEELINGS,    EMOTIONS,    AND   MOVEMENTS.  413 

limbs  and  derangement  of  speech  through  fear;  the  red- 
dening or  paling  which  express  anger,  disgust,  or  shame, 
etc. 

(2)  The  principle  of  the  association  of  analogous  sensa- 
tions emphasizes  such  facts  as  imply  that  sensations  having 
a  common  tone  of  feeling  combine  most  readily  and  thus 
strengthen  each  other.     In  this  manner,  both  mouth  and 
nose  express  in  company  the  disgust  or  pleasure  of  smells 
and  tastes ;  the  muscles  combine  with  the  skin  to  express 
certain  sensations  arising  through  irritation  of  the  latter, 
etc. 

(3)  The  principle  of   the  relation  of  particular  move- 
ments to  particular  perceptions  of  the  senses  is,  of  course, 
a  principle  of  the  broadest  application.     By  gestures  with 
the  eyes,  and  head,  and  limbs,  we  indicate  the  ideas  of 
extension  and  relation  in  space.     Care,  expectation,  exul- 
tation, depression,  throw  the  members  of  the  body  into 
expressive  postures,  which  correspond  to  the  perception  of 
the  objects  exciting  those  feelings.     It  is  under  this  prin- 
ciple  that  the  psycho-physical  science    of   the  comic,  of 
physiognomy,  etc.,  brings  a  great  number  of  facts. 

Recent  inquiries  have  elicited  the  interesting  and  impor- 
tant fact  that,  as  a  rule,  the  great  actors  actually  have  the 
feelings  and  ideas  present  in  their  consciousness,  which 
their  acting  expresses  with  such  wonderful  results.  Their 
power  is  the  power  to  put  themselves  in  the  appropriate 
condition  of  mind,  rather  than  the  power  merely  to  act  a 
part. 


CHAPTER   XVII. 

CONSCIOUSNESS,  MEMORY,    AND    WILL. 

INQUIRY  into  the  physical  basis  of  those  mental  processes 
which  are  ordinarily  classed  among  the  "  higher "  is,  of 
course,  peculiarly  interesting ;  but  it  is,  at  the  same  time, 
peculiarly  unproductive  of  well  assured  results.  The  psy- 
chology of  these  processes,  as  studied  from  the  introspective 
point  of  view,  has,  on  the  other  hand,  a  great  comparative 
advantage.  For  it  is  these  processes  which  best  submit 
themselves  to  introspection;  it  is  they  which  have  been 
most  carefully  and  successfully  studied  by  the  method  of 
introspection.  But  the  correlated  cerebral  processes  — 
even  if  we  admit  without  argument  that  such  processes 
exist  —  are  in  precisely  the  opposite  condition.  The  testi- 
mony of  the  most  learned  and  cautious  experts  in  phys- 
iology confirms  the  declaration,  that  such  a  thing  as  a 
definite  and  detailed  science  of  the  physical  functions  of 
the  hemispheres  of  the  brain  does  not  exist. 

We  have  previously  discovered  (see  Chapter  V.)  that  the 
so-called  "general  nerve-physiology"  of  the  nerve-muscle 
machine  is  in  a  very  incomplete  condition.  We  have 
also  seen  that  faint  and  doubtful  guesses,  conjectural 
modifications  of  general  laws  of  the  molecular  physics  of 
the  nervous  elements  (the  "  laws  "  themselves  being  largely 
conjectural),  comprise  the  answer  which  science  can  at 
present  give  as  to  the  behavior  of  that  vast  complex  of 
nerve-cells  and  nerve-fibres  which  constitutes  the  human 
brain. 

The  only  course  which  physiological  psychology  can 
414 


CONSCIOUSNESS,    MEMORY,    AND   WILL.  415 

adopt  in  attempting  to  deal  with  mental  phenomena  of 
the  so-called  higher  order  is,  then,  the  following:  The 
facts  of  consciousness  must  be  accepted  on  the  authority 
of  consciousness,  as  studied  by  the  method  of  introspective 
analysis ;  and  then  we  may  cautiously  speculate  as  to  their 
probable  physiological  correlates,  by  extending  the  conjec- 
tures of  general  nerve-physiology  to  the  cerebral  hemi- 
spheres. This  course  will  be  adopted  in  the  present  chapter. 
If  its  results  are  not  very  complete  and  defensible  through- 
out, the  fault  is  to  be  charged  to  the  account  of  the  subject 
rather  than  its  method  of  treatment. 

Nothing  which  has  just  been  said  should  be  understood 
as  detracting  from  the  value  of  experiment  in  testing  all 
theories  proposed  to  account  for  the  so-called  "higher" 
mental  phenomena.  It  must  not  be  forgotten,  however, 
that  what  the  experiments  themselves  immediately  give  us 
is  nothing  other  than  more,  and  perhaps  also  novel,  mental 
phenomena.  The  end  of  the  thread  which  we  securely 
hold  in  our  hand  always  consists  of  observed  data  of  con- 
sciousness. The  other  end,  the  correlated  physiological 
brain-processes,  is  always  hidden  from  our  observation. 
Nay  more ;  the  theory  of  what  it  is  that  constitutes  the 
peculiar  nature  of  these  processes  is  still  in  the  stage  of 
uncertain  conjecture.  And  what  it  is  that  serves  to  make 
brain-processes  a  fit  physical  basis  for  the  mental  phenom- 
ena, or  makes  the  conjectural  changes  of  these  processes 
fit  to  act  as  antecedents  or  causes  of  the  different  kinds  of 
mental  phenomena,  is  wholly  unknown. 

There  are  three  topics  under  this  general  head  to  which 
our  discussion,  from  lack  of  other  trustworthy  material, 
must  be  confined.  These  are  the  phenomena  ordinarily 
called  consciousness;  and  the  special  forms  of  conscious- 
ness called  memory  and  will. 


416  PHYSIOLOGICAL   PSYCHOLOGY 


PSYCHO-PHYSICAL   THEORY  OF  CONSCIOUSNESS. 

The  Nature  of  Consciousness.  —  From  the  point  of  view 
held  by  introspective  psycholog}-,  consciousness  cannot  be 
denned.  By  the  term  "  consciousness  "  we  mean  to  indi- 
cate the  most  general  fact  of  the  existence,  in  some  form, 
of  sentient  or  mental  life.  But  every  actual  expression  of 
mental  life  is  in  some  particular  form ;  it  is  a  "  state  "  or 
"  act "  of  consciousness.  In  other  words,  every  actual 
consciousness  defines  itself  by  some  content.  For  conscious- 
ness never  actually  is  consciousness  in  general,  —  an  activ- 
ity or  state  that  might  be  separated  from  all  individual 
state  or  process  of  consciousness,  without  content,  as  it 
were. 

Inasmuch,  then,  as  consciousness  is  the  condition  of  all 
internal  experience  whatever,  we  cannot  deduce  or  explain 
its  essential  nature  from  particular  forms  of  such  experi- 
ence. 

Consciousness,  or  the  general  fact  of  having  any  form  of 
sentient  life  in  distinction  from  being  unconscious  (as  in 
a  dreamless  sleep  or  "  dead  "  swoon),  must  also  be  distin- 
guished from  sgZ^-consciousness.  The  latter  is  the  con- 
scious attribution  of  any  particular  so-called  "  state  of  con- 
sciousness "  to  the  Ego,  or  subject  of  them  all.  That  is, 
self-consciousness  is  a  form  of  consciousness  characterized 
chiefly  by  the  nature  of  its  object  (the  Ego),  and  by  the 
peculiar  feeling  of  interest  which  fuses  with  the  apprehen- 
sion of  this  object. 

We  have  already  spoken  of  a  "  circuit  of  consciousness  " 
(p.  377),  and  of  the  number  of  objects  which  it  can  con- 
tain. Nothing  is  more  certain  or  familiar  in  our  experience 
with  ourselves  than  the  great  variations,  in  respect  to 
amount  of  energy,  degrees  of  clearness,  and  —  as  it  were 
—  height  of  attainment,  which  characterize  the  different 
states  of  consciousness.  To  represent  consciousness  as  an 


CONSCIOUSNESS,   MEMORY,    AND   WILL.  417 

attenuated  line,  with  no  breadth  or  possible  variation  in 
breadth,  is  most  misleading ;  and  yet  this  form  of  represen- 
tation has  been  the  accepted  one  with  a  large  number  of 
English  psychologists.  If  we  are  to  assist  our  imaginations 
to  a  knowledge  of  the  truth  by  such  partially  inapt  figures 
of  speech,  it  is  better  to  represent  the  "  field  of  conscious- 
ness "  by  a  series  of  overlapping  circles  having  a  large  pos- 
sible variation  in  their  diameters ;  or  by  what  we  see  of 
change  in  a  kaleidoscope  when  we  turn  it  slowly  before 
the  eye. 

The  Physical  Basis  of  Consciousness.  —  Little  can  be  added 
on  this  point  to  what  has  already  been  said  regarding  the 
physical  basis  of  the  different  forms  of  consciousness.  It 
has  been  concluded  that,  in  man's  case,  the  cerebrum  is 
probably  the  sole,  as  it  is  certainly  the  chief,  "  organ  "  of 
consciousness  (see  p.  179  f.).  By  this  we  can  mean  nothing 
intelligible,  however,  except  this :  that  the  constitution 
and  molecular  changes  of  the  nervous  matter  of  the  cere- 
brum are  the  only  immediate  antecedents  or  concomitants 
of  the  phenomena  of  consciousness ;  and  so  that,  whatever 
takes  place  in  the  body  outside  of  the  cerebrum  has  an  effect 
upon  consciousness  only  in  case  it  gets  itself  represented,  as 
it  were,  within  that  supreme  organ. 

A  recent  writer  (Herzen)  holds  that  the  physical  basis 
of  consciousness  rests  on  the  biological  law  which  condi- 
tions the  activity  of  a  tissue  on  its  decomposition  and 
ensuing  regeneration.  The  intensity  of  consciousness,  as  a 
neural  function,  depends  on  the  intensity  of  the  decompo- 
sition of  the  brain  tissue  ;  and  it  is  inversely  as  the  ease 
and  rapidity  with  which  the  inner  work  of  one  nerve-ele- 
ment is  transmitted  to  another.  This  theory  explains  some 
facts.  It  does  not  appear,  however,  that  the  amount  of 
the  work  of  decomposition  in  the  brain-tissue  is  a  measure 
of  the  breadth,  height,  and  depth,  of  the  field  of  con- 
sciousness. 


418  PHYSIOLOGICAL   PSYCHOLOGY. 

On  grounds  of  general  theory  it  is  very  probably  true 
that  the  physical  basis  of  any  consciousness  whatever  rests 
upon  a  certain  intensity,  in  the  appropriate  centres,  reached 
by  that  unknown  neural  process  for  which  these  centres 
are,  by  constitution  and  habit,  peculiarly  fitted.  But  any 
consciousness  is  always  some  particular  form  of  conscious- 
ness. Every  particular  form  of  consciousness  may  then 
be  said  to  have  its  basis  in  a  certain  intensity  of  the  neural 
processes  peculiar  to  those  centres,  whose  activity  is  cor- 
related with  that  one  form  of  consciousness. 

Physical  Conditions  of  Consciousness.  —  Among  the  known 
conditions  of  all  conscious  mental  activity  is  the  character 
and  amount  of  the  brain's  blood-supply.  To  stop  this 
supply  results  in  putting  an  end  for  the  time  to  all  con- 
sciousness ;  to  impede  or  corrupt  it  disturbs  and  depresses 
consciousness ;  to  alter  its  character  changes  the  character 
of  consciousness. 

Observation  of  man  and  the  lower  animals,  and  experi- 
ment on  the  animals  by  decapitation  and  otherwise,  have 
shown  that  the  condition  of  the  brain  is  anaemic  in  sleep. 
When  the  amount  and  time-rate  of  the  conscious  mental 
processes  are  lowered,  the  amount  of  arterial  blood  drawn 
to  the  higher  centres,  and  there  used  up,  is  diminished. 
Dr.  Cappie  has  propounded  the  theory  that  the  physical 
condition  of  consciousness,  as  distinguished  from  the 
unconsciousness  of  profound  slumber,  depends  upon  an 
excess  of  the  pressure  of  the  arterial  circulation  in  the 
brain  substance  over  the  pressure  of  the  venous  circulation 
in  the  pia  mater.  The  molecular  agitation  of  the  conscious 
mental  processes  draws  the  arterial  blood  through  the 
capillary  vessels,  like  the  draught  created  by  the  burning 
of  a  fire. 

Whatever  particular  theory  may  be  held  as  to  the  pre- 
cise nature  of  the  physical  basis  and  conditions  of  con- 
sciousness, thus  much  seems  undoubtedly  true.  That 


CONSCIOUSNESS,   MEMORY,   AND   WILL.  419 

peculiar  kind  of  "  work "  which  is  known  as  the  con- 
jectural molecular  agitation  of  the  nervous  substance  of 
the  higher  cerebral  centres  is  an  indispensable  condition, 
and  in  some  way  at  least  a  rough  measure,  of  the  so-called 
activity  or  intensity  of  consciousness.  Here  again,  how- 
ever, must  we  refer  to  the  very  indefinite  and  figurative 
way  in  which  we  can  use  the  terms  "  amount,"  "  intensity," 
"  measure,"  as  applied  to  states  of  mind. 

PSYCHO-PHYSICAL   THEORIES  OF  MEMORY. 

The  mental  phenomena  which  are  grouped  under  the 
general  term  of  "  Memory  "  offer  themselves,  in  a  tempting 
way,  to  explanations  derived  from  conjectural  principles  in 
"  general  nerve-physiology  "  and  in  the  special  physiology 
of  the  centres  of  the  cerebrum.  These  phenomena  are 
usually  understood  to  imply  three  powers,  or  phases  of  one 
power  of  the  mind.  They  are  (1)  retention,  (2)  repro- 
duction, and  (3)  recognition.  Of  the  three,  only  the  first 
two  seem  to  admit  of  even  a  conjectural  physiological 
explanation;  and  it  is  doubtful  whether  these  two,  con- 
sidered as  separated  (were  that  possible)  from  the  third, 
are  mental  processes  at  all.  "  Recognition,"  however,  is 
essentially  of  consciousness;  it  is  mental  and  cannot  be 
conceived  of  as  having  any  physical  representative  or 
correlate. 

Psychological  Theories  of  "Retention." — We  have  just 
said  that  the  "retention,"  which  is  commonly  spoken  of 
as  necessary  to  the  phenomena  of  memory,  cannot  be  con- 
sidered as  a  mental  act.  If  we  ask  ourselves,  Where  is 
the  idea  or  the  perception  I  once  had,  between  the  time  of 
original  experience  and  the  time  of  recall?  —  the  answer 
must  be:  The  "  idea  "or  the  "perception"  is  nowhere. 
It  does  not  exist  in  any  sense  of  the  word,  since  the  exist- 
ence of  an  "  idea  "  or  "  perception  "  consists  solely  in  its 
being  an  act  or  state  of  conscious  life. 


420  PHYSIOLOGICAL   PSYCHOLOGY. 

But  if  we  ask  ourselves,  What  are  those  changes  pro- 
duced by  stimulation  in  the  substance  of  the  brain,  which 
constitute  the  physical  basis  of  conscious  acts  of  memory, 
under  the  laws  of  habit  and  association  of  ideas  ?  —  we  ask 
a  question  which  is  perfectly  intelligible,  although  its  cor- 
rect answer  may  not  be  obtainable.  Three  forms  of  the 
physiological  theory  of  memory,  considered  as  "  retention," 
are  possible.  These  are:  (1)  Memory  depends  upon  a 
movement  persisting  in  the  brain;  (2)  it  depends  upon 
a  certain  residuum,  of  the  nature  of  a  "scar,"  or  fixed 
impression,  persisting  in  the  brain ;  or  (3)  it  depends  upon 
a  persistent  disposition,  or  tendency  to  movement  created 
in  the  brain.  All  such  terms  as  the  foregoing  are  probably 
used  somewhat  figuratively  when  applied  to  the  brain  sub- 
stance ;  precisely  what  they  fitly  represent  we  do  not  know. 
But  the  third  form  of  theory  has  most  evidence  in  its  favor. 
We  shall,  therefore,  present  the  arguments  in  its  behalf. 

Fading  of  the  Primary  Image.  —  It  is  difficult  to  draw  the 
line  betAveen  the  after-images  of  a  sensory  impression  and 
the  memory-images  (strictly  speaking)  of  the  same  impres- 
sion. The  thousands  of  faint  impressions  which  enter  into 
our  daily  life  seem  quickly  to  vanish  without  leaving  even 
a  trace  behind.  But  that  these  impressions  linger  for  a 
period  near,  or  under,  the  "threshold  of  consciousness" 
can  readily  be  shown.  If  we  are  called  upon  to  direct 
attention  upon  them,  to  fixate  and  describe  them,  within 
a  few  seconds  of  their  occurrence,  we  find  it  possible  to  do 
this.  Some  of  them  admit  of  such  recall  for  a  period  of 
several  minutes  after  their  occurrence.  But  if  not  atten- 
tively "  apperceived "  within  this  brief  time,  such  impres- 
sions usually  fade  away  beyond  all  recall. 

Relation  of  Retention  to  Time.  —  Let  a  line  of  given  length 
be  regarded,  for  a  brief  time,  then  removed,  and  after  a 
varying  interval  the  effort  made  to  recall  its  image  so  as 
to  compare  it  accurately  with  another  line  of  nearly  the 


CONSCIOUSNESS,   MEMORY,   AND   WILL.  421 

same  length.  It  will  be  found  that  the  clearness  of  the 
memory-image  of  the  visual  line  falls  off  quickly  at  first, 
then  more  slowly,  and  finally  approximates  a  stationary 
condition.  Let  a  tone  of  given  pitch  be  sounded,  and  then, 
after  a  brief  interval,  a  second  tone  of  the  same,  or  nearly 
the  same,  pitch.  In  such  a  case,  according  to  the  experi- 
ments of  H.  K.  Wolfe,  the  judgment  as  based,  in  part,  on 
the  memory-image  of  the  first  tone,  will  be  most  accurate 
at  an  interval  of  about  2  seconds.  For  a  longer  period 
than  2  seconds,  the  curve  of  memory  for  pitch  of  tones 
falls  off  pretty  regularly  as  the  interval  increases  to  be- 
tween 10  and  20  seconds ;  then  it  is  retarded  or  ceases  to 
decline ;  and,  further  beyond,  it  falls  off  still  more  rapidly 
with  increasing  time. 

That  patient  investigator,  Ebbinghaus,  found  that  the 
process  of  forgetting  a  series  of  "nonsense  syllables"  is 
rapid  at  first,  and  then  slower  afterwards.  After  an  hour's 
time  had  elapsed,  %  the  original  work  must  be  done  to 
relearn  the  series ;  after  8  hours,  f .  But  after  1  day  the 
impression  retained  about  -J  its  original  strength ;  after  6 
days,  i ;  after  30  days,  3-.  This  investigator  concluded  that 
the  ratio  of  what  is  retained  to  what  is  forgotten  is  in- 
versely as  the  logarithm  of  the  time. 

Persistence  of  Certain  After-images.  —  In  various  cases  of 
strong  or  repeated  impressions,  the  complete  or  partial 
after-images  recur  persistently  for  a  long  time  after  the 
impressions  have  ceased.  Prolonged  work  with  the  micro- 
scope causes  the  visual  images  seen  in  its  focus  to  live  "  in 
the  fundus  of  the  eye  "  ;  so  that,  after  several  hours,  shut- 
ting the  eyes  will  make  them  reappear  with  great  distinct- 
ness. Musicians,  after  musical  seances  or  after  giving 
instruction,  sometimes  hear  the  sounds  repeated  for  days. 
After  a  journey  on  a  railroad  car,  the  rattle  of  the  car  may 
persist  in  the  ears  for  a  long  time,  as  do  the'  sensations 


422  PHYSIOLOGICAL   PSYCHOLOGY. 

whose  impression  arises  in  muscles,  semi-circular  canals,  and 
other  internal  organs,  after  a  journey  by  sea. 

The  Physical  Basis  of  Retention,  —  Niepce  de  Saint- Victor 
has  shown  that  luminous  undulations  may  be  "  to  some 
extent  garnered  up  in  a  sheet  of  paper,"  ready  to  be  re- 
vealed at  the  call  of  special  reagents.  A  plate  of  dry 
collodion,  after  being  briefly  exposed  to  the  sun's  rays, 
retains  for  weeks  in  the  darkness  the  effects  of  the  inde- 
scribably delicate  changes  which  have  been  wrought  in  it. 
The  stimulation  of  certain  reagents  will  revive  the  images 
latent  in  such  a  plate.  The  well-seasoned  Cremona,  which 
has  been  played  upon  by  skilled  hands,  will  reproduce  the 
tones  with  superior  sweetness  and  purity,  on  account  of 
the  secret  molecular  changes  of  which  it  has  been  made 
the  subject  by  previous  agitations  from  the  bow  of  the  vio- 
linist. These  things,  however,  afford  us  only  analogies 
for  the  physiological  explanation  of  memory. 

It  is  to  distinctively  biological  facts  and  principles  that 
we  must  look  for  the  proper  explanation  of  the  mental 
phenomena  which  imply  so-called  "  retention."  The  fun- 
damental fact  seems  to  be  that  the  nerve-element  —  at 
least,  the  nerve-cell  which  is  concerned  in  psychical  pro- 
cesses (sometimes  called  the  "  psychic  nerve-cell  ")  —  is 
modified  in  a  permanent  manner  as  an  effect  of  its  excita- 
tion. We  have  already  considered  many  phenomena  which 
imply  this  general  fact.  Such  are  the  progressive  estab- 
lishment of  functional  centres  in  the  spinal  cord  and  brain 
of  a  young  animal  (for  example,  the  new-born  puppy),  the 
phenomena  of  substitution  in  the  localization  of  cerebral 
function,  and,  especially,  many  of  the  phenomena  of  apha- 
sia. The  same  thing  is  implied  in  that  acquired  skill 
which  results  in  "  learning,"  as  we  say,  so  as  without  con- 
scious judgment  and  choice  to  perform  feats  of  dexterity 
and  skill.  Indeed,  learning  to  walk,  to  talk,  to  sing,  etc., 
implies  the  same  principle.  All  habit,  acquired  in  the  con- 


CONSCIOUSNESS,    MEMORY,    AND   WILL.  423 

trol  of  the  organism,  tends  to  become  habit  of  purely 
organic  self-control. 

Now  the  nervous  system  is  a  vast  and  complicated 
molecular  mechanism,  all  coming  under  the  general  bio- 
logical law.  t  Moreover,  we  have  to  notice  that  the  nerve- 
cells,  modified  as  they  are  by  repeated  excitation,  preserve 
and  perpetuate  the  modification  under  the  biological  laws 
of  the  nutrition  of  living  organisms.  ^The  exercise  of  any 
group  of  nerve-cells  tends  to  procure  their  enlargement  by 
appropriation  of  the  nutriment  brought  to  them  in  the 
blood-supply.  And  when  these  cells,  thus  enlarged  and 
molecularly  altered  according  to  the  character  and  amount 
of  their  exercise,  multiply  themselves,  their  offspring  come 
under  the  general  principle  of  heredity  in  its  application 
to  all  living  mechanisms. 

The  precise  nature  of  the  molecular  modifications,  which 
are  thus  perpetuated  and  propagated  in  the  elements  of 
the  nervous  system,  is  unknown.  To  speak  of  them  as  "per- 
sistent vibrations,"  that  are  "  weaker  echoes  "  of  the  nerve- 
commotions  produced  by  the  original  stimulations,  seems 
to  us  neither  good  physics  nor  sound  physiological  psychol- 
ogy. They  are,  rather,  a  specially  complicated  instance  of 
the  general  biological  principles  of  modified  molecular  con- 
stitution, increased  nutrition,  and  inheritance  of  acquired 
characteristics. 

The  physical  basis  of  memory,  as  retentive,  is  therefore 
laid  in  the  habit,  or  acquired  tendency,  of  the  elements  of 
the  nervous  system.  This  tendency  has  respect  both  to 
the  individual  elements  and  to  the  association  of  groups  of 
these  elements.  Each  element  —  speaking  figuratively  — 
may  be  considered  as  a  minute  area  intersected  by  an 
indefinite  number  of  curves  of  different  directions  and 
orders.  Thus  a  molecular  commotion  in  any  such  area 
may  run  out  into  the  system  along  any  one  of  innumerable 


424  PHYSIOLOGICAL   PSYCHOLOGY. 

curves.     In  every  such  small  fragment  "  the  whole  curve 
slumbers." 

Physiological  Theories  of  Reproduction,  —  The  nature  of 
the  physical  basis  of  memory,  considered  as  reproductive, 
is  even  more  purely  conjectural  than  that  of  memory 
considered  as  retentive.  The  most  probable  conjectures, 
however,  are  those  which  follow  along  the  lines  already 
indicated.  A  perpetuation  of  persistent  and  similar  vibra- 
tions in  the  form  of  "  weaker  echoes  "  does  not  seem  prob- 
able. The  term,  "  dynamical  associations."  has  been  chosen 
by  one  writer  (M.  Ribot)  to  describe  those  tendencies  to 
allied  and  combined  action  which  become  established  in 
and  between  the  different  nerve-elements  and  cerebral 
centres. 

Another  writer  (Professor  Wm.  James)  has  expressed 
his  views  as  to  the  nature  of  the  physical  basis  for  the  laws 
of  association  as  follows  :  "  The  amount  of  activity  at  any 
given  point  in  the  brain  cortex  is  the  sum  of  the  tendency 
of  all  other  points  to  discharge  into  it,  —  such  tendencies 
being  proportionate  (1)  to  the  number  of  times  the  excite- 
ment of  each  other  point  may  have  coexisted  with  that  of 
the  point  in  question ;  (2)  to  the  intensity  of  such  excite- 
ments; and  (3)  to  the  absence  of  any  rival  locality  or 
process  functionally  disconnected  with  the  first  point,  into 
which  the  discharge  might  be  diverted."  "  Every  presen- 
tation," says  another  writer  (Fouille'e),  "tends  to  associate 
with  other  presentations  on  account  of  the  identity  of  their 
seat  in  the  brain.  .  .  .  Contiguity  in  time  links  things  only 
by  means  of  a  contiguity  in  extension  of  the  brain.  Thus 
are  established  in  the  nerve-paths,  as  on  the  railroads,  junc- 
tions analogous  to  those  where  the  switchman  determines 
the  course  of  the  trains."  [Is  there,  then,  something  to  be 
said  of  a  mental  "  switchman  "  determining  the  course  of 
these  trains  of  ideas  ?]  But  these,  and  all  similar  physio- 
logical theories  of  reproduction,  seem  to  us  far  too  simple 


CONSCIOUSNESS,   MEMORY,   AND   WILL.  425 

to  account  for  the  phenomena  as  we  have  real  experience 
of  them,  —  including  the  control  of  association  by  attention, 
by  sesthetical  and  ethical  and  other  interests,  and  that 
peculiar  accompanying  condition  of  conscious  memory 
called  recognition. 

Reproduction  involves  Forgetfulness.  —  "  To  live  is  to 
acquire  and  lose  ;  life  consists  of  dissolution  as  well  as 
assimilation.  Forgetfulness  is  dissolution."  This  is  true 
whether  we  consider  the  subject  from  the  mental  or  from 
the  physiological  point  of  view.  If  all  the  alterations  of 
the  intramolecular  constitution  of  the  nerve-cells  were 
alike  conserved  and  propagated,  and  if  all  the  "  dynamical 
associations  "  among  the  groups  and  centres  composed  of 
the  cells  were  always  alike  stable,  then  no  basis  could  exist 
for  specific  and  characteristic  reproduction  of  the  memory- 
images. 

In  the  phenomena  of  aphasia  we  see  how  temporary  or 
permanent  forgetfulness  of  classes  of  images,  or  of  definite 
and  particular  images,  may  be  due  to  functional  or  organic 
derangement  of  the  cerebral  centres.  The  same  thing,  in 
less  degree,  is  shown  in  the  loss  of  memory  caused  by  dis- 
turbances of  the  blood-supply  of  the  cerebral  centres. 
Moreover,  when  a  number  of  nerve-commotions,  arising  in 
different  associated  centres,  flow  together  and  inhibit  each 
other  in  a  certain  area,  loss  of  the  memory  of  objects  whose 
impressions  are  received  in  this  area  may  be  the  result. 
Whatever  interferes  with  the  working  of  the  so-called 
"  dynamical  associations  "  leads  to  confusion  or  forgetful- 
ness  of  the  memory-images.  On  the  other  hand,  whatever 
quickens  and  multiplies  the  working  of  these  associations 
results  in  acceleration  and  enlargement  of  the  circuit  of 
conscious  memory-images. 

Organ  of  Memory.  —  No  tenable  ground  exists  for  speak- 
ing of  a  special  organ  or  seat  of  memory.  Every  organ  — 
indeed,  every  cerebral  area  and  every  psychic  "  nerve-cell " 


426  PHYSIOLOGICAL  PSYCHOLOGY. 

—  has  its  own  memory.  What  Cardinal  Newman  once 
said  of  the  psychical  faculty  is  true  of  the  organic  basis : 
"  There  are  a  hundred  memories  as  there  are  a  hundred 
virtues."  Every  sense  and  every  so-called  faculty,  so  far 
as  it  comes  under  the  biological  laws  applying  to  retention 
and  reproduction  at  all,  does  so  in  the  particular  and 
definite  associated  areas  where  its  physical  basis  is  laid. 
There  is  sound  reason,  then,  for  speaking  of  a  "  memory  of 
the  ear,"  "  memory  of  the  eye.,"  etc. 

There  is,  then,  no  one  place  where  alone  memory  is  at 
home  in  the  brain.  Yet  the  memory  of  any  perception  of 
the  senses,  any  complex  state  of  feeling,  or  of  ideation, 
involves  a  large  number,  not  only  of  contiguous  nerve-ele- 
ments, but  of  more  or  less  remotely  allied  centres  of  the 
brain.  On  this  point  again  we  might  appeal  to  the  phe- 
nomena of  cerebral  localization,  —  especially  of  aphasia  and 
other  pathological  phenomena.  This  is  true  even  of  those 
cases  where  some  particular  date  or  name  seems  to  slip 
away  beyond  the  power  of  recall.  For  example,  we  have 
record  of  a  patient  who,  after  a  fever,  lost  all  knowledge 
of  the  letter  F. 

Complexity  of  the  Mental  Phenomena.  —  The  laws  of  repro- 
duction, or  of  the  so-called  association  of  ideas,  have  been 
the  subject  of  curious  and  painstaking  interest  for  hundreds 
of  years.  Probably  no  other  subject  in  introspective  psychol- 
ogy has  received  so  much'  attention.  In  the  attempt  to 
simplify,  the  claim  has  repeatedly  been  made  that  they  could 
all  be  reduced  to  a  small  number  of  principles,  —  perhaps 
even  to  a  single  law,  like  the  "  law  of  contiguity "  or  the 
"  law  of  redintegration."  We  shall  not  enter  this  contro- 
verted field;  it  lies  apart  from  the  researches  special  to 
physiological  psychology.  In  our  judgment,  however,  the 
allied  experimental  and  physiological  researches  indicate 
that  the  number  of  principles  concerned  in  the  reproduc- 


CONSCIOUSNESS,    MEMORY,    AND   WILL.  427 

tion  of  mental  images  must  be  greatly  increased  rather 
than  diminished. 

The  researches  of  Ebbinghaus  into  the  principles  regu- 
lating his  own  power  to  learn  and  to  remember  series  of 
"  nonsense  syllables  "  (see  p.  421)  led  him  to  emphasize 
two  pre-eminent  sources  of  influence  over  the  mental  train 
of  reproduced  images.  These  were  (1)  changes  in  the  con- 
centration of  attention ;  and  (2)  unconscious  influence  from 
theories  and  opinions.  But  if  this  be  so,  how  immensely 
complex  and  profound  must  be  the  reasons  which  control 
the  reproductive  energy  of  the  entire  life  of  any  individual 
mind!  All  the  psychical,  and  all  the  biological,  history 
of  each  individual  expresses  itself  in  every  act  of  repro- 
duction. 

The  great  complexity  of  the  phenomena  of  associated 
reproduction  of  mental  images  may  be  further  illustrated 
by  the  answer  to  the  following  question :  When  a  series 
a  b  c  d  efg  has  been  learned,  does  a  recall  5,  and  b  recall 
<?,  and  so  on ;  or  does  a  recall  5,  and  tend  also  to  recall  <?,  d, 
and  the  rest?  In  other  words,  do  the  bonds  of  association 
which  unite  the  memory-images  extend  below  conscious- 
ness, as  it  were,  though  in  a  diminishing  degree,  to  all  the 
distant  members  once  held  together  in  the  "  circuit  of  con- 
sciousness "  ?  The  researches  of  Ebbinghaus  answer  this 
question  affirmatively.  Learning  once  a  series  of  even  16 
"  nonsense  syllables  "  saves  time  on  attempting  to  relearn 
this  series,  in  whatever  manner  its  members,  when  relearned, 
are  related  to  each  other.  The  strength  of  association,  as 
measured  by  this  saving  of  time  in  relearning,  is  indicated 
by  the  following  table  :  — 

Per  cent. 

Saving  of  time  on  relearning  is,  between  contiguous  members  .  33.3 
Saving  of  time  on  relearning  is,  skipping  one  syllable  ....  10.8 
Saving  of  time  on  relearning  is,  skipping  two  syllables  ....  7.0 
Saving  of  time  on  relearning  is,  skipping  three  syllables  ...  5.8 
Saving  of  time  on  relearning  is,  skipping  four  syllables  ....  3.3 


428  PHYSIOLOGICAL  PSYCHOLOGY. 

Experiment  shows  also  that  the  bonds  of  association  ex- 
tend backward — though  with  an  inferior  degree  of  strength 
—  as  well  as  forward.  The  same  researches  placed  the 
saving  of  time  in  relearning,  with  inversion  only,  at  12.4 
per  cent. ;  with  inversion  and  skipping  of  one  syllable,  at 
5  per  cent. 

A  reference  to  the  fact  that  reaction-time  is  lengthened 
by  increasing  the  complication  and  unusual  character  of 
the  association  processes,  and  shortened  by  practice  and 
attention,  reinforces  the  same  conclusion.  In  reviving 
established  associations  of  ideas  the  entire  mental  history  is 
involved.  But  in  forming  new  associations,  especially,  as 
well  as  also  in  reproducing  the  established  ones,  tempera- 
ment, disposition,  and  conscious  regard  for  utilitarian, 
ethical,  and  sesthetical  interests,  are  potent  influences. 

The  complexity  of  the  phenomena  called  "  mental '' 
doubtless  implies  a  somewhat  corresponding  complication 
of  the  brain-processes  concerned  in  the  reproduction  of 
memory-images.  In  brief,  the  adult  brain  is  a  system  of 
vastly  intricate  and  interrelated  molecular  mechanisms. 
It  has  been,  during  its  entire  history,  in  the  process  of  vital 
organization  of  these  intricate  interrelations.  The  par- 
ticular brain-processes  concerned  in  each  act  of  reproduc- 
tion all  fall  under  the  laws  which  control  the  general 
biological  process  of  perpetual  organization.  The  mental 
phenomena  are  a  series  of  related  "  circuits  of  conscious- 
ness," —  overlapping  and  fading  into  each  other.  The  brain- 
processes  are  a  succession  of  related  nerve-commotions  in 
centres  contiguous  and  distant,  —  also  overlapping  and 
fading  into  each  other. 

The  Psychical  Act  of  Conscious  Recognition.  —  The  fore- 
going conjectures  have  to  do  with  the  explanation  only 
of  what  is  sometimes  called  an  "  organic  memory/'  But 
so-called  "  organic  memory ''  is  a  purely  physical  affair. 
It  is  utterly  lacking  in  the  power  to  suggest  an  explana- 


CONSCIOUSNESS,   MEMORY,   AND   WILL.  429 

tion  for  that  conscious  recognition  which  is  the  peculiarity, 
and  the  peculiarly  baffling  mystery,  of  memory  as  a  truly 
mental  affair.  Let  us  then  consider  what  is  involved  when 
/  remember  this  or  that,  —  as  we  are  wont  to  say. 

The  experience  of  consciousness  is  one  of  a  constantly 
changing  succession  of  states.  The  rise  and  fall  of  vol- 
untary or  involuntary  attention,  and  the  change  in  its 
direction,  are  accompanied  by  —  rather  are  factors  in  —  a 
constant  shifting  of  the  phases  and  circuit  of  conscious- 
ness. But  of  these  shifting  mental  complexes,  some  bear 
a  most  peculiar  mark.  In  their  very  nature  they  claim  to 
reproduce  distant  and  past  phases  or  circuits  of  conscious- 
ness. They  are,  sui  generis,  "  representative  "  of  the  past. 
But  of  whose  past  ?  for  there  is  no  circuit  of  consciousness, 
regarded  as  previously  completed,  that  must  not  be  attrib- 
uted to  some  Ego,  some  mind.  And  there  is  no  memory- 
image,  claiming  to  represent  such  circuit  of  consciousness, 
that  does  not  involve  the  conscious  recognition  of  that 
particular  image,  as  representative  of  its  own  past,  by  the 
same  mind.  These  fundamental  truths  are  not  in  the  least 
affected  by  any  actual  or  conceivable  mistakes  of  memory. 
They  simply  describe  the  actual  and  indisputable  pecul- 
iarity of  that  factor  of  conscious  recognition  which  belongs, 
sui  generis,  to  memory  as  a  psychical  act. 

This  peculiar  and  mysterious  claim  of  the  memory- 
image,  to  represent  my  past  state  (of  perception,  feeling, 
thought,  etc.)  is  not,  strictly  speaking,  verifiable  by  an  act 
of  comparison.  Were  I  to  attempt  this,  the  perception  of 
the  object,  renewed  for  purposes  of  comparison,  would  be 
a  new  perception,  — •  another  and  different  mental  act ;  and 
the  memory-image,  revived  for  purposes  of  comparison, 
would  be  a  new  reproduction,  involving  the  mystery  of 
memory,  as  conscious  recognition,  in  the  same  inexplicable 
form. 

We  cannot  even  conceive  of  the  nature  of  a  physiologi- 


430  PHYSIOLOGICAL   PSYCHOLOGY. 

cal  process  which  would  serve  as  an  "  explanation  "  in  any 
sense  of  the  word,  for  this  characteristic  of  recognition, 
this  self-appropriation  as  belonging  to  the  past  of  the  same 
Ego,  or  mind,  which  enters  into  all  conscious  memory. 
All  that  any  physiological  process  could  possibly  explain, 
in  case  we  knew  its  nature  most  completely,  would  be  why 
I  remember  one  thing  rather  than  another  —  granted  the 
inexplicable  power  of  the  mind  to  remember  (consciously  to 
recognize  the  present  state  as  representative  of  its  own 
past)  at  all.  We  repeat  then  the  declaration  of  several 
years  ago  :  "  This  power  is  a  spiritual  activity  wholly  sui 
generis,  and  incapable  of  being  conceived  of  as  flowing  out 
of  any  physical  condition  or  mode  of  energy  whatever." 

The  connection  of  Attention,  both  voluntary  and  invol- 
untary, with  the  phenomena  of  reproduction  under  the 
law  of  association,  is  manifest.  The  discussion  of  mem- 
ory leads  us  therefore  to  consider,  — 

PSYCHO-PHYSICAL   THEORIES  OF   WILL. 

Several  of  the  topics  already  discussed  have  included 
those  phenomena  in  which  so-called  "  acts  of  will "  take 
part  as  factors.  This  is  true  of  "  psycho-physical  reac- 
tion-time," and  its  lengthening  or  shortening  according  as 
it  does  or  does  not  contain  a  choice  between  methods  of 
reaction  (see  p.  371  f.).  It  is  also  especially  true  of  the 
effect  of  voluntary  attention  upon  the  bodily  movements, 
and  upon  the  associated  ideas  which  constitute  the  men- 
tal train  (see  p.  410  f .).  From  the  very  first,  the  experi- 
ments and  theories  of  physiological  psychology  have  been 
turned  toward  the  consideration  of  the  "  will."  The  inter- 
est which  such  inquiries  awaken,  on  account  of  their  con- 
nection with  problems  in  ethical  philosophy  and  in  the 
philosophy  of  religion,  is  too  obvious  to  need  more  than  a 
mere  mention.  Our  general  purpose,  however,  leads  us  to 


CONSCIOUSNESS,   MEMORY,   AND   WILL.  431 

limit  the  discussion  of  the  subject  to  those  few  points 
upon  which  some  experimental  evidence,  however  meagre, 
can  be  gathered  from  the  department  of  science  we  are 
exploring. 

General  Physical  Basis  of  Acts  of  Will.  —  If  we  use  the 
general  term  "will"  to  describe  all  those  mental  phenom- 
ena which  seem  to  secure  the  conscious  direction  or  control 
of  the  bodily  movements  or  of  the  mental  train,  we  may 
make  a  probable  assertion  respecting  their  general  physi- 
cal basis.  This  basis  is,  especially,  that  power  of  automa- 
tism which  is  concentrated,  so  to  speak,  in  the  nerve-cells 
of  the  central  nervous  system,  "  Automatism,"  or  the 
power  of  originating  molecular  changes  which  cannot  be 
explained  Avholly  by  reference  to  the  transmitted  influence 
of  external  stimuli,  belongs  to  all  living  protoplasm.  It  is 
on  the  basis  of  this  fact  that,  as  it  is  sometimes  said,  an 
amoeba  has  "  a  will  of  its  own." 

The  attempt  has  been  repeatedly  and  persistently  made 
to  refer  all  the  phenomena  of  living  organisms  to  the  order 
known  as  the  "sensory-motor  reflexes"  (see  p.  135 f.). 
Recently  this  attempt  has  been  extended  (particularly  by 
Miinsterberg  and  others)  so  as  to  include,  without  exception, 
all  the  highest  psycho-physical  processes.  The  principal 
justification  of  the  thorough-going  character  of  this  attempt 
is  our  ignorance,  and  the  desire  to  establish  a  single  con- 
sistent theory  for  all  cases  of  vital  activity.  But  so  long 
as  physiology  utterly  fails  to  bring  even  the  movements  of 
a  minute  amoeboid  speck,  or  the  behavior  of  the  spinal 
cord  of  a  decapitated  frog,  under  any  theory  of  "  sensory- 
motor  reflexes,"  we  shall  have  (a  fortiori)  to  acknowledge 
that  the  power  of  automatism  belongs,  in  a  peculiar  way 
and  high  degree,  to  the  cerebral  centres. 

No  Special  Organ  of  Will.  —  It  has  already  been  shown 
that  "  organic  memory  "  is  not  a  property  of  any  one  ner- 
vous centre,  or  group  of  centres,  located  in  the  brain.  The 


432  PHYSIOLOGICAL   PSYCHOLOGY. 

same  thing  is  true  of  that  property  of  automatism  in  which 
we  find  the  physical  basis  of  will.  Every  centre  of  the 
nervous  system  which  is  capable  of  originating  molecular 
changes  in  response  to  internal  stimuli  may  be  an  organ 
of  will  so-called. 

But  an  act  of  the  will  is  always  an  act  of  some  particular 
kind.  There  can  be  no  volition  to  motion  in  general ;  but 
only  a  volition  denned  and  limited  to  the  movement  of 
certain  limbs,  or  of  the  trunk  including  the  limbs,  with  a 
certain  direction  and  degree  of  motion.  Thus  also  every 
act  of  will,  for  the  clearer  "  apperception "  of  some  object 
in  the  circuit  of  consciousness,  or  for  the  control  of  the 
mental  train,  is  necessarily  limited  and  defined.  And  the 
physicarbasis  of  each  act  of  will  is  laid  in  the  appropriate 
physiological  action  of  those  centres  of  ideation,  apper- 
ception and  motion,  which  are  concerned  in  that  particular 
act  of  will.  Whenever  an  act  of  will  takes  place,  then  at  the 
cerebral  areas  which  are  correlated  with  that  particular  act, 
the  appropriate  molecular  changes  arise  in  the  "psychic 
nerve-cells" 

Kinds  of  Acts  of  Will.  —  From  the  point  of  view  held  by 
the  student  of  ethics,  it  may  seem  incorrect  and  even 
absurd  to  deny  freedom  to  any  so-called  "  act  of  will."  But 
from  the  point  of  view  taken  by  physiological  psychology 
the  whole  matter  presents  itself  in  a  different  light.  We 
have  already  spoken  of  involuntary  movements,  that  are 
not  impulsive,  and  of  forced  acts  of  attention  (see  p.  408  f.). 
Both  these  phenomena  imply  "  uni-motived "  acts  of  will ; 
that  is,  acts  of  will  where  there  is  no  consciousness  of 
acting  freely  or  of  exercising  choice,  but  rather  the 
contrary. 

On  the  other  hand,  there  are  acts  of  will  which  involve 
an  indefinite  amount  of  antecedent  deliberation,  of  weigh- 
ing of  reasons  and  motives,  and  final  choice  made  with  the 
clearest  conviction  that  it  is  our  responsible  and  free 


CONSCIOUSNESS,   MEMORY,   AND    WILL.  433 

action.  And  between  these  two  extremes  there  are  all 
degrees  of  the  rational  and  voluntary  factors  in  different 
so-called  "acts  of  will."  A  psychology,  which  is  true  to 
experience,  is  compelled  to  admit  that  what  we  prize  as 
freedom  of  will  is  a  matter  of  development,  with  an  infi- 
nite variety  of  degrees.  But  what  corresponding  provision 
shall  physiology  suggest  as  necessary  for  those  different 
processes  that  constitute  the  physical  conditions  of  these 
phenomena?  Only  one  answer  seems  to  us  defensible. 
It  is  this :  a  brain,  developing  under  biological  laws,  and 
standing  in  its  peculiar  relation  to  the  unfolding  of  the  life 
of  consciousness,  with  an  infinite  variety  of  ways  of  blending 
reflex  sensory-motor  and  automatic  processes  in  its  allied 
centres. 

Every  so-called  act  of  will  is  then  the  expression  of  the 
combination  of  several  kinds  of  physiological  processes, 
accomplished  in  the  centres  of  the  brain.  These  may 
include  (1)  sensory  excitations  coming  from  one  or  more 
of  the  end-organs  of  sense ;  (2)  reciprocal  excitement  of 
allied  cerebral  centres  in  which  the  processes  concerned  in 
the  appropriate  perceptions  and  memory-images,  with  their 
accompanying  tones  of  feeling,  are  taking  place ;  (3)  ten- 
tative and  anticipatory  motor  impulses  which  mark  the 
felt  tendency  to  innervate  particular  groups  of  muscles; 
and,  finally,  (4)  a  certain  automatic  activity  of  particular 
nerve-centres  under  influence  from  the  mental  phenomena 
we  call  "choice,"-  — a  thing  which  physiological  science  is 
wholly  unable  to  explain  but  not  competent  to  deny. 

It  is  the  resultant  of  these  combining  processes  which 
represents  on  the  physiological  side,  the  complex  conditions 
of  the  "  so-called  acts  of  will."  These  acts,  as  they  appear 
in  consciousness,  are  characterized  by  corresponding  psy- 
chical characteristics.  (1)  They  may  be  more  or  less 
mechanically  controlled  or  forced  by  the  intensity  of  sen- 
sation ;  (2)  they  may  comprise  a  larger  or  smaller  number 


434  PHYSIOLOGICAL  PSYCHOLOGY. 

of  clear  or  confused  perceptions  and  memory-images  with 
differing  intensities  of  different  kinds  and  tones  of  feel- 
ing ;  (3)  they  may  involve  inchoate  and  anticipatory  feel- 
ings of  effort,  or  strain,  that  signify  the  drawing  of  attention, 
the  rising  in  consciousness  of  a  nisus,  in  one  or  more  of 
several  directions ;  (4)  they  may  culminate,  as  it  were,  in 
a  decided  choice,  with  its  accompanying  and  following 
conviction  that  this  act  is,  in  a  peculiar  and  even  unique 
manner,  our  own. 

It  is,  of  course,  the  factor  of  choice  —  No.  (4)  —  which 
we  designate  as  pre-eminently  belonging  to  will.  Choice  is 
not,  indeed,  the  whole  of  will.  There  can  be  no  act  of  the 
mind  as  will,  in  the  highest  meaning  of  the  words,  which 
does  not  involve  all  the  other  above-mentioned  sets  of  fac- 
tors, both  psychical  and  physiological.  Choice  is,  how- 
ever, the  central  and  distinguishing  factor  of  those  acts 
which  deserve,  above  all  others,  to  be  ascribed  to  the 
inner  and  independent  life  of  the  conscious  mind.  In 
the  popular  imagination  —  and  we  believe  justly  —  choice 
implies  a  real  influence  of  the  mind  over  the  body. 

In  terms  of  psycho-physical  science :  The  existence  of 
those  states  of  consciousness,  which  are  known  to  the  sub- 
ject of  them  as  his  choice,  determines  the  arising  of  appro- 
priate and  correlated  molecular  changes  in  the  higher  and 
controlling  centres  of  the  brain.  If  this  fact  is  ultimate 
and  inexplicable,  it  is  not,  on  that  account,  to  be  disputed 
as  a  fact.  The  evidence  for  this  fact,  from  experimental 
and  physiological  psychology,  is  by  no  means  small.  We 
shall  now  present  it  —  though  only  briefly  and  in  part. 

Dependence  of  Sensation  and  Perception  on  Will.  —  Many 
things  which  we  clearly  perceive,  or  intensely  feel,  or 
vividly  remember  or  imagine,  we  cannot  —  as  we  say  — 
"  help  "  attending  to.  The  sudden  flashing  of  a  light,  or 
the  passing  of  a  bright  object  across  the  field  of  vision,  the 
unexpected  loud  noise,  the  smells  in  the  atmosphere,  the 


CONSCIOUSNESS,   MEMORY,    AND   WILL.  435 

tastes  of  our  food,  the  sensations  of  the  skin  or  internal 
organs,  force  themselves  upon  attention.  Such  phenomena 
tend  to  confirm  the  crude  statement,  recently  renewed 
with  manifold  assertions  and  imposing  array  of  argument, 
by  Dr.  Miinsterberg :  "  The  will  is  only  a  complex  of  sen- 
sations." The  act  of  will,  even  in  its  highest  form,  is  to 
be  explained  —  this  authority  argues  —  as  a  sensory-motor 
process,  by  the  ordinary  presuppositions  of  natural  science, 
and  without  the  help  of  any  immaterial  principle. 

But  there  are  other  phenomena  which  defy  such  easy- 
going attempts  at  solution  of  the  mystery  of  body  and 
mind.  [The  diminishing  of  discernment-time  by  voluntary 
attention  has  already  been  remarked  (p.  371).]  When,  for 
example,  we  are  attending  to  any  sensation  which  is  peri- 
odically repeated  but  very  weak,  fluctuations  in  its  inten- 
sity constantly  tend  to  occur.  Thus  a  black  radius  on  a 
white  disk,  when  revolving,  can  be  made  to  lengthen  and 
shorten  alternately.  So  the  ticking  of  a  watch  can,  by 
placing  its  distance  aright,  be  made  somewhat  rhythmically 
to  alternate  between  audible  and  inaudible.  Now  if  atten- 
tion, when  directed  to  the  sensation,  is  left  to  itself,  as  it 
were,  it  will  vacillate  with  a  regular  periodicity  —  the 
explanation  of  which  is  not  quite  clear,  and  the  length  of 
which  differs  for  different  senses  and  under  different  cir- 
cumstances. But  voluntary  and  concentrated  self-directed 
attention  influences  this  period. 

By  voluntary  attention  we  can  intensify  a  sensation,  and 
make  clearer  a  perception  or  idea,  in  consciousness.  We 
incline,  indeed,  to  attend  to  the  stronger  of  two  excitations 
of  sense ;  but,  within  certain  limits,  we  can  attend  where 
we  will.  We  incline  to  attend  to  objects  lying  in  the  point 
of  regard  of  the  visual  field ;  but  we  can  will  to  attend  to 
objects  lying  in  the  outward  portion  of  this  field.  By  vol- 
untary attention  we  can  bring  into  clear  consciousness  the 
otherwise  invisible  double  images.  Some  experimenters 


436  PHYSIOLOGICAL   PSYCHOLOGY. 

with  the  phenomena  of  "  conflict  of  colors,"  when  a  green 
image  is  formed  on  one  eye  and  a  red  on  the  other,  can  see 
either,  or  combine  the  two,  at  will. 

The  analysis  of  complex  sensations  or  perceptions  may 
also  be  performed  at  will.  Voluntary  concentration  of 
attention  is  necessary  for  the  musician  to  hear  the  over- 
tones which  combine  with  the  fundamental  tone  to  consti- 
tute a  "  clang."  In  mastering  any  complex  visual  object, 
the  fixation  and  wandering  of  the  point  of  regard  is,  to  a 
certain  extent,  under  the  control  of  will.  On  waking  grad- 
ually from  sleep,  our  surroundings  become  more  and  more 
clearly  defined  to  eye,  ear,  and  skin,  as  the  grade  of 
voluntary  attention  in  analysis  and  discernment  rises. 
Voluntary  concentration  of  attention,  not  infrequently, 
completely  dispels  the  illusions  of  sense.  In  expectation 
of  a  particular  sense-impression,  concentrated  voluntary 
attention  may  so  affect  the  cerebral  centres  as  to  anticipate 
the  expected  perception ;  it  may  so  intensify  some  weaker 
similar  impression  as  to  cause  it  to  be  mistaken  for  the 
expected  impression. 

In  fact,  all  experience  is  full  of  similar  facts.  All  lan- 
guage implies  them.  We  cannot  say,  with  emphasis, 
Listen !  or  Look  !  —  instead  of  Did  you  hear  or  see  ?  — 
without  witnessing  to  the  influence  upon  the  organism  of 
the  mental  act  of  choosing  to  attend  to  a  particular  sensa- 
tion or  perception. 

Closely  connected  with,  and  indeed  involved  in,  phe- 
nomena like  the  foregoing  are  the  following  facts,  which 
bear  witness  to  the  influence  of  Will  over  the  cerebral 
centres. 

Dependence  of  Muscular  Movement  and  Tension  on  Will.  — 
No  one  is  disposed  to  dispute  that  a  large  portion  of  our 
muscular  movement,  or  muscular  tension  in  the  direction 
of  movement,  is   reflexly  or   impulsively  originated.     In 
such  cases  there  is  no  question  as  to  the  dependence  of 


CONSCIOUSNESS,    MEMORY,    AND   WILL.      .  437 

the  cerebral  centres  as  regards  the  psychical  operation 
of  conscious  choice.  It  is  undoubtedly  also  true  that 
the  muscles  cannot  be  voluntarily  innervated  unless  they 
have  been  previously  called  into  action  reflexly  or  impul- 
sively, so  as  to  furnish  sensation-complexes  and  mem- 
ory-images of  such  complexes,  to  serve  as  the  objects 
for  voluntary  attention  and  choice  (compare  p.  411).  We 
have  also  affirmed  the  opinion  that  the  so-called  feelings 
of  effort  and  strain  originate  at  the  periphery  of  the  body, 
in  the  conditions  of  skin,  muscles,  tendons,  and  joints.  If 
we  had  only  such  phenomena  of  muscular  movement  to 
discuss,  we  might  satisfy  the  demand  for  explanation  by 
denying  the  influence  of  choice  upon  the  cerebral  centres 
and  through  them  upon  the  muscles  of  the  body. 

But  there  is  a  large  class  of  phenomena  —  both  involved 
in  ordinary  experience  and  elicited  by  experiment  —  which 
plainly  belong  to  another  order.  We  can,  within  certain 
limits,  decide  "  at  will "  —  as  we  say  —  the  speed,  energy, 
rhythm,  and  magnitude  of  muscular  contraction,  and  so 
the  complexity  and  form  of  the  resulting  movements. 
This  we  do  whenever  we  raise  a  weight,  for  example,  by 
estimating  in  units  of  whatever  standard  of  sense  the  char- 
acter and  amount  of  innervation  of  the  muscles  required 
to  raise  it.  All  deliberate  and  rational  control  of  our 
bodily  organs  —  and  such  control  enters  into  the  entire 
conscious  life  of  apperception  and  representation  —  im- 
plies, and  depends  upon,  the  use  of  this  power. 

But  we  have  also  the  unique  and  mysterious  power  of 
inhibiting  the  muscular  movements  which  would  otherwise 
be  called  forth  by  external  and  internal  stimuli.  On  this 
point  Gad  has  shown  that  the  reflex  stimulation  of  the 
eyelids  with  vapor  of  ammonia  can  be  voluntarily  inhib- 
ited; Briicke  and  others  have  demonstrated  our  power 
at  will,  to  weaken  the  effect  of  the  direct  stimulation  of  a 
muscle  by  electricity ;  Eichhorst  has  called  attention  to  the 


438  PHYSIOLOGICAL   PSYCHOLOGY. 

fact  that  the  trembling  of  palsy  can  be  partially  suppressed, 
if  the  sybject  choose. 

The  terms  "  unique  and  mysterious  "  have  just  been 
applied  to  this  power  of  inhibition  at  will.  Recent  experi- 
ments have  seemed  to  disprove  that  this  power  consists  in 
the  innervation  of  muscles  antagonistic  to  those  called  into 
action  by  the  impulses  reflexly  originated.  For  there  are 
muscles  under  the  control  of  will  that  have  no  antago- 
nistic muscles.  The  muscle  used  in  accommodation  of  the 
eye  is  a  typical  instance  of  such  an  "  autonomous  "  muscle. 
The  facial  nerve,  which,  of  all  the  motor  nerves,  has  the 
most  direct  anatomical  connection  with  the  higher  motor 
centres,  controls  muscular  action  in  the  same  way.  What 
a  "  servant  of  the  soul,"  for  the  voluntary  and  involuntary 
expression  of  the  life  of  the  soul,  is  here  employed ! 

Now  the  reaction-time  of  inhibition,  after  brief  practice, 
appears  not  to  differ  from  that  of  direct  impulse.  On  vary- 
ing the  tension  and  amplitude  of  the  muscular  excursion, 
the  change  in  the  "  inhibition-time  "  follows  closely  upon 
the  change  in  "impulse-time."  It  is  a  legitimate  conclu- 
sion, then,  that  the  paths  in  which  the  physiological  basis 
of  will  runs,  are  identical  for  both  impulsive  and  inhibi- 
tory volitions.  It  would  seem  that  the  place  where  the 
nerve-waves,  which  originate  the  inhibition,  interfere  with 
the  nerve-waves  which  would  otherwise  originate  the  reflex- 
motor  impulse,  is  the  common  "psycho-motor"  centre. 
The  direct  voluntary  control  over  the  muscle,  to  modify 
or  to  diminish  the  amount  of  its  contraction,  is,  there- 
fore, the  expression  of  the  influence  of  the  will  over  this 
"  psycho-motor  "  centre. 

Dependence  of  the  Memory-images  upon  Will.  —  No  part  of 
our  complex  mental  life  appears  to  be  so  completely  a 
matter  of  mechanism,  conducted  before  the  conscious  mind 
rather  than  ly  it,  as  does  the  so-called  association  of  ideas. 
This  fact  has  already  been  made  prominent  by  the  phe- 


CONSCIOUSNESS,   MEMORY,    AND   WILL.  439 

nomena  of  reaction-time  (see  p.  375  f.).  But  even  in  this 
part  of  mental  life,  the  effect  of  voluntary  attention  and 
of  conscious  choice  is  unmistakable.  This  effect  may, 
indeed,  be  so  great  as  to  impart  to  the  memory-images  the 
vividness  of  perceptions,  by  intensifying  them  and  defi- 
nitely localizing  them  anew  in  the  organs  by  which  their 
originals  were  formed.  This  fact  connects  this  form  of 
activity,  springing  from  will,  with  the  voluntary  influence 
of  sensation  and  perception. 

Artists  in  kinds  of  art  which  involve  a  special  suscep- 
tibility and  activity  of  certain  of  the  senses,  are,  of  course, 
also  gifted  with  a  specialized  creative  and  reproductive 
energy  of  imagination.  Some  classes  of  mental  images 
tend  to  force  themselves  upon  us  all,  whether  we  will,  or 
not.  But,  on  the  other  hand,  we  can  all  seize  upon  par- 
ticular mental  images,  at  will ;  and  by  concentrating 
attention  upon  them  can  clarify  and  strengthen  them. 
The  artist's  weakness  and  his  voluntary  power  are  both 
special  in  these  regards.  Moreover,  one  can  surrender 
one's  self  to  a  comparatively  passive  attitude  before  the 
train  of  associated  ideas,  —  as  when,  for  example,  one 
indulges  in  reverie  and  day-dreaming.  Or  one  (within 
certain  limits)  can  say,  to  these  ideas :  Begone  from  con- 
sciousness !  and  one  can  enforce  one's  will  by  concen- 
trating attention  on  objects  of  perception,  or  by  turning 
into  other  lines  the  mental  train. 

Rhythm  of  Attention  in  Perception  and  Association.  —  We 
have  already  seen  that  weak  sensations  tend  to  rise  and 
fall  below  the  "  threshold  of  consciousness  "  in  a  periodic 
way;  in  other  words,  they  fluctuate  rhythmically  in  con- 
sciousness. This  period  is  different  for  different  sensa- 
tions ;  for  example  —  as  given  by  N.  Lange  —  it  is  3.4 
sec.  for  optic  vacillations,  and  not  less  than  4.0  sec.,  for 
acoustic.  The  fluctuations  of  sensation  this  observer 
attributes  to  fluctuations  in  attention  dependent  upon 


440  PHYSIOLOGICAL   PSYCHOLOGY. 

exhaustion  of  the  cerebral  centres.  This  explanation,  so 
far  as  the  assumption  that  voluntary  attention  directly 
influences  the  cerebral  centres  to  exhausting  molecular 
energy,  we  esteem  correct  beyond  doubt.  Although  it  has 
been  shown  recently  (by  Miinsterberg)  that  peripheral 
changes  also  have  a  great,  and  even  a  determining  influ- 
ence, over  the  occurrence  and  the  periodicity  of  these 
fluctuations. 

During  his  experiments  in  learning  and  relearning 
"  nonsense  syllables  "  Ebbinghaus  found  indications  of  a 
remarkable  rhythm  in  attention.  There  is,  he  thinks,  a 
periodic  oscillation. of  the  mental  susceptibility  to  intense 
concentration  of  attention,  in  which  "  the  increasing  fatigue 
seems  to  vary  about  a  gradually  shifting  middle  position." 
Thus,  in  84  experiments  with  six  16-syllable  series,  the 
mean  time  for  learning  the  1st  series  was  191  sec. ;  for  the 
2d,  224  sec. ;  for  the  3d,  206  sec. ;  for  the  4th,  218  sec. ; 
for  the  5th,  210  sec. ;  for  the  6th,  213  sec.  Such  a  result 
can  scarcely  be  due  to  anything  else  than  a  periodic 
exhaustion  and  recovery  of  the  cerebral  centres  under  the 
influence  of  attention  as  an  act  of  will. 

Phenomena  like  the  foregoing  are  often  appealed  to  in 
proof  of  the  complete  dependence  of  the  so-called  free 
choice  to  attend  upon  the  condition  of  the  nerve-centres  of 
the  brain.  As  to  a  dependence  in  this  direction,  there  need 
be  no  doubt.  But  the  primary  and  really  astonishing  fact 
is  that  the  mind's  choice  to  attend  exhausts  the  cerebral 
centres  by  making  them  do  intense  and  concentrated  work. 
The  dependence  of  the  activity  of  the  "psycho-motor  "  centres 
upon  the  purely  psychical  phenomenon  of  voluntary  choice  to 
attend  is  the  most  important  and  marvellous  of  all  psycho- 
physical  facts. 

The  Experiments  of  Miinsterberg.  —  This  investigator  has 
already  been  quoted  as  holding  that  will  is  nothing  but  a 
"complex  of  sensations,"  a  "definite  grouping  of  sensa- 


CONSCIOUSNESS,   MEMORY,    AND   WILL.  441 

tions,"  etc.  Now,  from  the  point  of  view  of  self-conscious- 
ness nothing  can  well  be  more  false  and  misleading  than 
such  statements  as  these.  It  is  precisely  this  which  we  do 
not  mean  when,  without  having  been  prejudiced  by  so- 
called  psycho-physical  science  (?),  we  candidly  state  our 
conscious  experience.  The  words  "  I  will,"  or  "  I  choose," 
have  a  perfectly  definite  meaning  as  describing  an  activity 
of  the  mind;  and  this  meaning  is  markedly  different  from 
that  which  we  give  to  the  words  "  I  have  this  or  that  set 
of  feelings  or  sensations." 

Most  students  of  physiological  psychology  who  deny 
that  the  mind  is  capable  of  real  choice,  but  affirm  rather 
that  what  appears  in  consciousness  as  its  choice  is  really  a 
definite  sensation-complex  "  dictated  to  it  by  the  cunning 
conjurer,  the  brain,"  attempt  to  base  their  opinions  on  an 
induction  from  facts.  This  Dr.  Miinsterberg  attempts. 
In  our  judgment  —  and,  for  the  present,  granting  the 
accuracy  of  his  experimental  data — the  attempt  fails.  His 
experiments  show  that  the  time  of  a  free  association  is 
briefer  than  that  of  a  limited  association  (the  type  of  the 
latter  being  as  follows  :  Given  a  general  term,  to  name  an 
instance  under  it).  They  show  that  a  "question-answer 
association  "  (e.g.  On  what  river  is  Cologne  ?)  is  also  briefer 
than  that  of  a  limited  association.  But  these  facts  may 
reasonably  be  held  to  be  due  to  the  general  truth  that  it 
does  take  time  to  initiate  those  cerebral  processes  which 
are  correlated  with  deliberate  intelligent  choice. 

It  may  also  be  admitted  that  Miinsterberg's  experiments 
add  strength  to  the  opinion  that,  in  complex  associations, 
both  the  mental  and  the  cerebral  processes  regularly  over- 
lap. "  The  mind  is  not  a  point  through  which  each  process 
must  pass  in  turn,  but  is  a  place  in  which  the  most  com- 
plex interactions  have  their  play."  And  certainly  the 
brain  is  very  far  from  being  a  point.  This  admission  is 
indicative  of  the  exceedingly  subtile  and  complex  relations 


442  PHYSIOLOGICAL  PSYCHOLOGY. 

which  exist  between  the  different  cerebral  centres,  and 
between  these  centres  and  the  mind. 

We  know  of  no  evidence  from  the  experiments  of  phys- 
iological psychology  which  proves  anything  against  the 
possibility  of  what  consciousness  testifies  to,  —  namely,  a 
real  psychical  phenomenon,  unique  and  different  from  all 
mere  definite  content  of  sensation  and  mental  images, 
which  is,  in  the  order  of  nature,  a  determining  factor  for 
the  excitation  of  the  "  psycho-motor  "  areas  of  the  brain. 

Special  Physiological  Conditions  of  Choice. — What  happens 
in  the  brain  when,  after  two  or  more  conflicting  presenta- 
tions of  sense,  or  conflicting  ideas,  and  a  period  of  delibera- 
tion, one  of  them  is  made  the  object  of  choice  ?  In  answer 
to  a  similar  question  a  celebrated  physiologist  responded 
some  years  since :  "  We  know  absolutely  nothing."  Of  the 
physiological  processes  which  accompany  the  mental  prep- 
aration of  the  choice,  it  would  seem  that  either  one  of  two 
things  may  be  true.  The  more  intense  of  the  conflicting 
processes  may  prevail  over  the  others  and  gain  possession 
—  as  it  were — of  the  appropriate  " ps}^cho-motor  centres"; 
or  the  several  processes  may  persist  and  interpenetrate. 
An  example  of  this  kind  of  alternative  may  be  taken  from 
the  phenomena  of  the  "conflict  of  colors."  But,  looked 
at  from  the  point  of  view  of  consciousness,  it  is  obvious 
that  the  will,  or  choice  of  the  mind,  may  decide  a  question 
of  conflicting  perceptions  or  ideas.  What  precise  physio- 
logical process  corresponds  to  this  psychical  act  of  choice, 
-  the  mental  phenomenon  of  decision  after  deliberation  ? 
The  same  confession  of  ignorance  quoted  above  seems  to 
exhaust  the  subject. 

We  have  seen  that  the  effect  of  voluntary  attention  is 
most  marked  upon  the  cerebral  centres.  By  it  some  of 
them  appear  to  have  their  molecular  energy  relatively 
depressed;  and  others  are  relatively  heightened.  By  it 
the  entire  mechanism  of  the  brain  may  be  called  upon  for 


CONSCIOUSNESS,   MEMORY,    AND   WILL.  443 

a  rapid  conversion  into  kinetic  form  of  the  stored  energy 
of  its  nerve-cells.  Thus,  under  the  influence  of  attention 
the  entire  cerebrum  (and  the  different  cerebral  centres 
with  varying  relative  degrees)  is  put  into  a  condition  of 
changed  susceptibility  to  external  and  internal  stimuli,  as 
well  as  to  the  discharge  of  "  psycho-motor  "  energy  along 
the  various  efferent  nerve-tracts.  Concentrated  voluntary 
attention  implies  a  large  amount  of  work  in  process  of 
accomplishment,  within  the  cerebral  centres.  The  feelings 
of  strain  and  exhaustion,  the  profuse  sweating  which  often 
accompanies  experiments  in  reaction-time,  are  in  testimony 
on  this  point. 

Choice  is  —  as  every  one  knows  —  followed  by  a  sense 
of  relief  from  strain ;  it  is  apparently  significant  of  the  sub- 
sidence of  that  condition  of  conflicting  states  of  tension 
and  nerve-commotion  which  has,  before  the  consummation 
of  choice,  prevailed  in  certain  cerebral  areas.  But,  as  has 
already  been  twice  said,  precisely  what  it  is  that  is  brought 
about  by  will  (or  the  mind  making  a  choice),  physiological 
science  cannot  say.  Nor  does  such  science  furnish  the 
slightest  valid  ground  for  the  assertion  that  the  choice  is 
not,  what  it  appears  in  consciousness  as  being,  —  a  psychi- 
cal occurrence  that  determines  the  adjustment  of  physical 
relations  between  the  parts  of  the  bodily  organs.  This 
adjustment  is,  however,  not  primarily  one  of  the  visible 
and  gross  masses  of  this  organism,  but  of  the  molecular 
conditions  and  activities  of  those  "psycho-motor"  areas 
which  control  these  masses. 

Physical  Basis  of  the  "  Higher  Powers."  —  We  decline  to 
enter  upon  the  discussion  of  the  question :  What  special 
molecular  conditions  and  activities  are  correlated  with  the 
mental  processes  called  "abstraction,"  "generalization," 
etc. ;  or  with  the  higher  sesthetical  and  ethical  feelings  and 
ideas ;  or  with  those  norms  of  all  rational  life  which 
philosophy  has  been  wont  to  call  the  "  intuitions  "  or  the 


444  PHYSIOLOGICAL  PSYCHOLOGY. 

"  categories  "  of  the  mind  ?  Upon  these  subjects  our  igno- 
rance is  not  only  profound,  but  also  —  it  would  appear  — 
hopeless.  No  other  higher  wisdom  in  this  field  is  known 
to  physiological  psychology  than  that  illustrated  in  the  fol- 
lowing quotation  from  Lotze  :  "  For  all  the  higher  spiritual 
faculties,  which  consist  in  judgment  of  the  relations  of 
given  conceptions,  we  neither  know  how  empirically  to 
demonstrate  a  definite  bodily  organ,  nor  should  we  know 
how  to  conceive  precisely  what,  that  is  of  any  use,  such  an 
organ  could  contribute  toward  the  solution  of  the  problem 
—  that  is,  the  pronouncing  of  the  judgment  itself.  It  is 
conceivable,  on  the  other  hand,  that  these  higher  activities 
might  presuppose  the  complete  and  clear  representation 
of  the  content  about  which  the  judgment  is  to  be  passed, 
and,  consequently  also  the  undisturbed  function  of  those 
organs  which  contribute,  first,  to  perception  by  the  senses ; 
then  to  reproduction  and  combination  with  other  percep- 
tions ;  and,  finally,  to  the  appropriate  attachment  of  feelings 
of  value  to  each  of  them." 


CHAPTER   XVIII. 
AGE,  SEX,  AND  TEMPERAMENT. 

THE  relations  between  mental  states  and  physiological 
conditions  and  activities,  which  have  been  thus  far  exam- 
ined, are  in  general  subject  to  sudden  alterations.  From 
moment  to  moment  of  our  daily  life  the  quantity,  quality, 
time-order,  and  mental  combination,  of  our  sensations  are 
dependent  upon  the  amount,  kind,  rate,  and  conjunction  or 
opposition  of  the  stimuli.  When,  however,  we  consider  the 
psycho-physical  theories  of  memory  and  will,  as  well  as  of 
mental  moods,  we  find  more  relations  of  a  statical  character 
established  between  mind  and  body. 

There  are  certain  relations  of  the  mental  phenomena  to 
the  physical  basis  which  change  their  character  very 
slowly,  or  do  not  change  at  all.  One  cannot  alter  one's 
sex,  parentage,  or  race-inheritance.  -In  the  correlated 
development  of  the  body  and  mind,  as  dependent  upon 
the  time  of  life,  marked  changes  come,  for  the  most  part, 
only  gradually.  Here,  however,  epochs  of  change  occur 
in  both  sets  of  characteristics,  such  as  emphasize  the 
dependence  of  the  latter  upon  the  former.  A  genuine 
and  clearly  marked  "  temperament "  may  be  combated 
successfully ;  but  the  fact  of  the  struggle  reveals  that 
firm  possession  of  the  seat  of  influence  over  mental  life 
which  certain  obscure  inherited  physical  traits  customarily 
maintain. 

It  is  these  "  statical "  relations  between  the  life  of  mind 
and  its  bodily  basis  which  we  now  propose  briefly  to  exam- 
ine. The  examination  will  only  include  the  three  points,  of 

445 


446  PHYSIOLOGICAL   PSYCHOLOGY. 

Age,  Sex,  and  Temperament.  On  all  these  subjects  the  col- 
lection of  data  involves  an  exploration  of  wide  and  uncer- 
tain fields.  The  entire  investigation  is,  indeed,  rather 
anthropological  than  strictly  physiological  or  psychological 
in  its  nature.  In  both  the  physical  and  the  psychical  series 
there  are  necessarily  many  gaps  and  deficiencies.  The  con- 
clusions—  if  such  they  can  be  called  —  must  be  received 
with  this  understanding. 

RELATION  OF  MIND  AND  BODY  DEPENDENT  UPON  AGE. 

Prenatal  Physical  Development.  —  The  growth  of  struc- 
ture, and  the  unfolding  of  physiological  function,  in  the 
unborn  human  being  have  been,  more  or  less  success- 
fully, investigated  by  embryology.  Yet  this  biological 
science  gains  most  of  its  knowledge  of  the  human  foetus 
from  study  of  the  lower  animals.  Certain  large  and  elabo- 
rate organs,  such  as  the  lungs,  the  eyes,  the  ears,  etc.,  are 
formed  under  morphological  conditions  and  influences 
with  which  we  are  imperfectly  acquainted,  but  without 
any  corresponding  psychical  development. 

The  brain  and  the  organs  of  sense,  several  weeks  after 
birth,  are  apparently  very  little  different  from  the  same 
structures  at  birth.  Yet  a  marked  change  in  the  mental 
life  of  the  child  has  undoubtedly  taken  place.  It  is  a  fair 
conjecture,  based  upon  grounds  of  "  general  nerve-physiol- 
ogy," that  some  corresponding  change  has  taken  place  in 
the  cerebral  areas.  Doubtless  the  molecular  alterations 
and  so-called  "dynamical  associations,"  which  constitute 
the  basis  of  the  memory  as  retentive  and  reproductive,  are 
chief  factors  in  this  cerebral  change.  It  is  certain  that 
many  of  the  structural  and  physiological  changes  which 
form  the  more  intimate  foundation  for  spiritual  activities 
are  secured  only  indirectly  in  the  central  organs  through 
the  cultivation  given  to  these  organs  by  the  use  of  the 
end-organs  of  sense  and  motion.  As  Soltmann  and  others 


AGE,   SEX,   AND   TEMPERAMENT.  447 

have  found,  stimulation  of  the  motor  areas  of  the  brain  of 
new-born  animals  does  not  produce  the  definitely  localized 
movements  usually  obtained  from  the  adult  animal.  The 
use  of  eye  and  hand,  in  their  connected  activity,  by  the 
new-born  child  educates  his  brain  greatly  in  the  few  weeks 
just  following  birth.  The  dependence  of  mind  and  brain, 
preceding  birth  as  well  as  afterwards,  is  presumably  indi- 
rect and  very  complex. 

Prenatal  Psychical  Development.  —  Concerning  the  psy- 
chology of  the  unborn  human  being  we  can  speak  with 
little  confidence.  Of  sensations  of  smell,  taste,  hearing, 
and  sight?  there  can  be  no  question  raised.  The  end- 
organs  of  these  senses  are  developed  at  birth ;  but  up  to 
this  time  they  have  not  been  active  so  as  to  arouse  the 
soul  to  the  sensations  of  which  they  supply  the  required 
stimuli.  Neither  can  those  sensation-complexes,  derived 
from  the  irritation  of  the  skin,  muscles,  tendons,  and  joints, 
on  which  the  perception  of  things  extended  and  external 
depends,  become  highly  developed  before  birth. 

It  is  perhaps  a  reasonable  conjecture  which  assigns  to 
the  psychical  life  of  the  unborn  infant  certain  sensations 
of  pressure  and  temperature,  for  the  most  part  transient 
and  disconnected,  occasioned  by  the  changing  conditions 
and  positions  in  the  mother's  womb.  If  we  are  to  speak 
of  prenatal  experience,  this  low  grade  of  consciousness  can 
as  little  be  accurately  represented  by  any  conscious  state  of 
the  human  adult  as  can  the  consciousness  of  the  animals 
to  which  the  structure  and  functions  of  the  body  of  the 
foetus,  in  succession,  bear  more  or  less  of  resemblance. 

Dependence  of  Height  on  Age.  —  It  has  been  estimated 
that  the  growth  of  the  foetus  in  length  for  the  six  months 
preceding  birth  is  regular;  and  that  it  averages  about 
54  mm.  a  month.  The  mean  length  at  birth  of  100  infants, 
measured  in  Brussels,  was  found  to  be  0.501  m.  (or  about 
19f  in.)  for  boys,  and  0.491  m.  (or  about  19|  in.)  for 


448  PHYSIOLOGICAL   PSYCHOLOGY. 

girls.  For  900  adults,  in  age  from  19  to  30,  the  mean 
height  was  1.6648-1.6841  m.  The  average  height  of  80 
students  at  Cambridge,  England,  was  1.768  m.  As  is  well 
known,  the  absolute  height  of  adult  man  varies  greatly  in 
different  regions  and  races,  and  under  different  conditions 
of  climate,  food,  etc. 

If  we  express  the  facts  by  the  fraction  of  the  whole 
height  previously  attained  which  the- growth  of  each  year 
attains,  the  figures  are  as  follows :  for  the  first  year,  about 
| ;  for  the  second,  | ;  for  the  third,  ^  5  f°r  the  fourth,  -^ ; 
for  the  fifth,  y1^ ;  for  the  sixth,  -j^,  etc.  From  this  time  to 
the  age  of  puberty  the  annual  increase  is  nearly  regular 
at  about  56  mm.  Shortly  before  or  during  the  period  of 
puberty,  a  sudden  rise  in  the  curve  of  growth  occurs ;  but 
after  this  period  the  curve  falls  off  until  about  the  age  of 
twenty-five,  when  maturity  of  height  may  be  considered 
as  attained.  A  very  slight  increase  continues  in  most 
cases  until  about  fifty,  when  a  decrease  —  especially  in  old 
age  —  occurs. 

The  psychical  life  of  perception  and  will  is,  of  course, 
dependent  to  a  large  extent  upon  the  height  and  gross 
bulk  of  the  body.  The  knowledge  of  magnitudes  and 
solidity  of  things,  and  the  cultivation  of  the  feelings  of 
"  Self  "  as  a  causal  agency,  as  well  as  that  "  diremption  " 
of  experience  which  organizes  all  the  world  into  "  my  sen- 
tient organism  "  as  set  over  opposite  to  other  "  things,"  are, 
in  a  general  way,  dependent  upon  growth  in  height.  The 
sarfie  remarks  also  apply  to  the  following  allied  develop- 
ment. 

Dependence  of  Weight  on  Age.  —  Like  the  height,  the 
weight  at  birth  also  differs  greatly  according  to  parentage, 
prenatal  conditions  of  nutrition,  etc.  The  average  weight 
of  new-born  infants,  as  ascertained  in  Brussels  and  also  as 
given  in  the  French  "  Dictionary  of  Medical  Sciences,"  is 
about  3.055  kilo.,  or  6.T35  Ibs.  avoirdupois.  One  year  after 


AGE,    SEX,    AND   TEMPERAMENT.  449 

birth  the  weight  has,  on  the  average,  been  tripled ;  in  six 
years  more  it  has  been  doubled  again,  and  in  thirteen  years 
quadrupled.  At  about  nineteen  the  mean  weight  of  both 
sexes  is  about  the  same  as  that  of  old  age.  The  maximum 
weight  of  the  male  is  attained,  as  a  rule,  about  forty ;  that 
of  the  female,  somewhat  later.  At  sixty  the  average 
weight,  like  the  height,  begins  to  diminish. 

The  psychical  development  is  indirectly  involved  in  the 
weight  of  the  body  as  dependent  upon  age.  This  is  par- 
ticularly true  of  those  sensations  and  cognate  feelings 
which  are  connected  with  the  poise  and  movement  of  the 
body,  with  its  slower  or  more  rapid  adjustment  to  the 
changing  relations  of  objects  in  space.  The  entire  mental 
movement  of  the  child  is,  in  a  measure,  typified  by  the 
agility  of  its  bodily  movements.  The  "feelings  of  posi- 
tion," which  belong  to  maturity  of  bodily  size  and  weight 
have  in  middle  life  reached  the  culmination  of  precision 
and  strength  combined  with  speed.  In  all  these  regards 
the  psychical  life  of  old  age  suffers  a  decline  which  is  vis- 
ibly manifested  in  feebleness  and  slowness  of  bodily  move- 
ments. 

More  indirectly  still,  and  yet  with  great  force  and  extent 
of  application,  does  the  same  principle  concern  the  moral 
and  sesthetical  feelings.  The  mind,  acting  as  so-called  will, 
is  always,  even  in  its  highest  forms  of  emotion  and  choice, 
interlocked  with  conditions  that  proceed  directly  from  the 
conditions  of  the  bodily  basis.  The  tempo  of  life,  and  char- 
acter of  the  strain  to  which  its  movement  answers,  are  not 
the  same  for  all  its  phases. 

Eelative  Proportions  among  the  Different  Organs.  —  The  size 
of  the  different  bodily  organs  —  both  absolute  and  relative 
—  varies  greatly  for  the  different  ages  of  life ;  but  their 
relative  size  remains  nearly  the  same  for  all  persons,  not 
obviously  deformed,  of  the  same  age.  The  most  essential 
parts  are  least  subject  to  any  wide  departures  from  the 


450  PHYSIOLOGICAL   PSYCHOLOGY. 

normal  type.  At  birth  the  length  of  the  head  is  about 
half  that  attained  on  complete  development  —  or  an  aver- 
age of  about  111  mm.  (4.37  in.).  It  reaches  about  154  mm. 
by  the  end  of  the  first  year,  and  173  by  the  end  of  the  sec- 
ond. This  growth  of  62  mm.  in  two  years  exceeds  all  sub- 
sequent growth.  The  developed  adult  head  is  about,  on 
the  average,  228  mm.  long,  or  1  to  !  of  the  entire  length  of 
the  body. 

The  facts  just  mentioned  show  that  the  increasing  size 
of  the  head  and  of  its  contents  of  nervous  matter,  is  cor- 
related, not  so  much  with  absolute  attainments  of  mental 
sort,  as  with  mental  exercise  and  growth  in  mental  powers. 
The  same  truth  appears  in  such  measurements  of  the  heads 
of  those  engaged  in  the  work  of  students  as  have  recently 
been  conducted  by  Galton  and  others. 

The  development  of  back  and  legs  and  muscles,  in 
the  child,  is  relatively  very  different  from  that  of  the 
head.  The  back  has  at  birth  only  about  J-  its  subsequent 
length ;  the  arm,  J ;  the  leg,  up  to  the  place  of  its  bifurca- 
tion, only  about  ^.  The  infant's  foot  (which  will  probably, 
if  it  be  the  foot  of  a  civilized  female,  never  again  appear 
in  its  natural  proportions)  is  about  the  same  length  as  the 
head,  —  about  -f  of  the  body.  The  hand  is  about  -J.  of  the 
length  of  the  body.  Unlike  the  head,  the  limbs  grow 
rapidly  after  the  second  year.  At  the  age  of  puberty 
they  are  greatly  lengthened  at  the  expense  of  their  trans- 
verse proportions. 

The  following  table  shows  the  relative  weight  of  the 
internal  organs  at  birth  and  after  maturity :  — 


AGE,    SEX,    AND   TEMPERAMENT. 


451 


ORGAN. 

PERCENTAGE  OF  BODY-WEIGHT. 

RATIO   or    THE 

TWO,   THE   IN- 
FANT     TAKEN 
ASl. 

Infant  at  birth. 

Adult. 

Skeleton      
Muscles,  etc  
Lungs     
Heart      .     .     . 

16.70 

23.40 
2.16 
0.89 
11.30 
0.28 
14.34 

15.35 
43.10 
2.01 
0.52 
6.30 
0.028 
2.37 

26 

£8 
20 
15 
12 
1.7 
3.7 

Skin  .'.•'.     .     . 

Eve 

Brain      

Dependence  of  Metabolism  on  Age. —  To  make  the  rapid 
growths  of  the  first  years,  a  great  amount  of  food,  repre- 
senting a  great  amount  of  potential  energy,  must  be  con- 
verted into  living  tissue.  This  more  rapid  metabolism 
of  the  infant  is  partly  demanded  in  order  to  keep  up  the 
normal  temperature  of  the  body,  which  is  slightly  higher 
(0.3°)  than  that  of  the  adult.  The  infant's  body  also  loses 
heat  much  faster  on  account  of  its  extremely  vascular  skin. 
Most  of  the  metabolism  is  directed,  however,  toward  the 
construction  of  living  tissue. 

The  heart  of  the  infant  is  much  larger,  in  relation  to 
the  entire  body,  than  is  the  heart  of  the  adult  (see  Table). 
The  whole  circuit  of  the  circulatory  system  is  traversed 
in  about  12  seconds,  while  the  time  necessary  in  the  case 
of  the  adult  is  about  22  seconds.  The  heart-beat  is  at  first 
about  130-140  per  minute,  —  falling  off  to  about  110  in 
the  second  year,  and  to  about  90  in  the  tenth.  The  res- 
piration is  about  35  per  minute  at  first,  28  in  the  second 
year,  and  26  in  the  fifth. 

Everything  in  the  infant  indicates,  therefore,  a  mobile 
and  flexible  condition  of  the  bodily  organs,  with  a  rela- 
tively large  development  already  secured  to  the  most  im- 
portant parts  of  the  nervous  system.  .A  scarcity  of  formed 


452  PHYSIOLOGICAL  PSYCHOLOGY. 

bodily, and  mental  habits  is  indicated.  The  lines  of  habit- 
ual action  of  the  mechanism  have  not  as  yet  been  marked 
out.  Habits  of  mental  sort,  as  connected  with  established 
dynamical  associations  among  the  nerve-elements  and  cen- 
tres of  the  brain,  are  as  yet  unformed. 

Psychical  Development  of  the  Infant.  —  The  large  size  and 
advanced  development  of  the  brain  and  end-organs  of 
sense  at  birth  are  indicative  of  mental  potentialities  rather 
than  of  the  actual  mental  life.  If  we  use  the  word 
"  mental "  to  designate  the  phenomena  of  consciousness, 
it  is  difficult  to  trace  the  earliest  mental  development. 
The  eyes  of  the  child  during  the  first  days  are  seldom  open 
for  any  length  of  time.  Perception  by  sight  implies  asso- 
ciated and  co-ordinated  movement  of  the  eyes,  with  the 
possibility  of  voluntary  fixation  or  wandering  of  the  point 
of  regard.  There  appears  to  be  considerable  difference  in 
the  length  of  time  after  birth  which  is  required  to  estab- 
lish these  necessary  conditions.  But  the  factors  required 
in  such  development,  as  well  as  the  stages  by  which  it 
advances,  have  already  been  sufficiently  discussed  (see 
Chapter  XIV.). 

All  newly  born  children,  since  there  is  no  air  in  the 
tympanum  previous  to  respiration,  are  deaf.  Children  dif- 
fer greatly  as  respects  the  age  at  which  they  give  sure 
tokens  of  having  sensations  of  sound.  The  reflex  excita- 
bility of  the  skin  of  the  infant,  in  spite  of  its  delicate 
character,  is  much  inferior  to  that  of  the  adult.  It  is  only 
under  gradual  cultivation  that  it  learns  to  respond  in  the 
maturer  forms  of  this  "geometrical  sense."  Taste  and 
smell,  considered  as  sensations  void  of  all  perceptive  char- 
acter, apparently  belong  to  the  first  days  of  the  infant's 
life. 

After  full  maturity  has  been  reached,  or  decline  of  the 
bodily  powers  has  begun,  the  mental  activities  are  less 
aggressive  and  acquisitive.  But  the  period  of  more  imme- 


AGE,   SEX,   AND   TEMPERAMENT.  453 

diate  dependence  of  these  activities  upon  the  lower  sensory- 
motor  apparatus  has  passed.  The  lines  of  both  bodily  and 
spiritual  habit  have  become  firmly  drawn.  Experience  is 
stored;  judgment  has  been  trained,  and  is  less  liable  to 
sudden  assaults  from  impulse. 

RELATIVE  DEVELOPMENT  OF  THE  SEXES. 

While  the  dependence  of  the  mental  development  upon 
the  condition  and  growth  of  the  bodily  organs,  as  affected 
by  age,  is  substantially  the  same  for  all,  certain  important 
differences  separate  the  sexes. 

Relative  Height  and  Weight  of  the  Sexes.  —  The  curve  of 
growth  from  birth  onward  runs  somewhat  differently  for 
the  male  and  female  child.  Before  maturity  the  height 
of  the  two  is  about  as  1  to  0.988 ;  at  maturity  it  is  about 
as  1  to  0.937  or  16  to  15.  The  absolute  height  of  the 
European  adult  male  is  1.467-1.890  m.  (about  4  ft.  11  in. 
to  6  ft.  4  in.)  ;  that  of  the  female,  1.444-1.740  m.  (or  4  ft. 
10  in.  to  5  ft.  10  in.).  But  at  the  age  of  sixteen  the  growth 
of  the  girl  is  as  far  advanced  as  that  of  the  boy  at  eighteen 
or  nineteen. 

The  relative  weight  of  the  two  sexes  does  not  follow 
exactly  the  same  rule  as  their  height.  At  birth  the  differ- 
ence is  about  0.6  Ib.  avoirdupois.  But  although  the  boy 
is  born  heavier,  at  twelve  the  two  sexes  have  nearly 
the  same  average  weight.  Woman  attains  her  maximum 
weight  several  years  later  than  man.  For  normally  formed 
and  well-nourished  men  the  limits  are  about  49.1-98.5  kilo. 
(108-217  Ibs.)  ;  for  women,  39.8-93.8  kilo.  (98-207  Ibs.). 

Relative  Proportions  of  the  Bodily  Members  of  the  Sexes.  — 
Even  in  early  childhood  sexual  differences  become  observ- 
able, as  respects  the  proportions  of  the  bodily  parts.  The 
bony  framework  of  the  boy  is  more  prominent  and  the  out- 
lines of  the  limbs  indicate  agile  and  strong  movement. 
Roundness  of  limbs  and  amplitude  of  flesh  cover  the  girl's 


454  PHYSIOLOGICAL  PSYCHOLOGY. 

framework.  The  formation  of  the  pelvis  in  the  two  is 
unlike;  and  the  centre  of  the  line  of  length  falls  on  a 
different  part  of  the  body.  The  chest  of  the  adult  male 
is  more  developed ;  his  breathing  is  lower  down ;  his  rate 
of  pulse  and  respiration  less  rapid.  The  length  of  his 
arms  stretched  out  is  about  1.045  of  his  height;  of  the 
female,  it  is  only  1.015.  The  relative  length  of  the  legs 
is  greater ;  and  the  circumferences  of  the  various  parts  of 
his  body  are  differently  proportioned.  His  step  is  to  hers 
as  1.157  to  1.000. 

The  average  physical  energy  of  which  the  male  is  capa- 
ble is  much  the  greater,  —  whether  it  be  measured  by  lift- 
ing weights,  by  pressure  with  the  hands,  or  other  ways  of 
producing  mechanical  effects.  Before  puberty  this  differ- 
ence has  been  estimated  as  expressed  by  the  ratio  3:2; 
afterward  by  the  ratio  9:5,  or  even  greater.  The  average 
boy  of  nine  or  ten  years  can  support  himself  for  some  time 
with  his  hands ;  the  girl  cannot.  The  average  man  can 
lift  some  154  kilo. ;  the  woman  scarcely  half  as  much. 

The  metabolism  of  the  female,  whether  measured  by  the 
respiratory  or  other  excreta,  is  both  absolutely  and  rela- 
tively less  than  that  of  the  male. ,  Her  blood  is  less  in 
quantity,  of  lighter  specific  gravity,  and  contains  fewer 
red  corpuscles. 

More  important  differences  concern  the  nervous  systems 
of  the  two  sexes.  The  weight  of  the  female's  brain,  as 
compared  with  that  of  the  male,  is  about  as  1.272:1.424. 
The  embryology  of  the  two  serves  to  show  a  difference  in 
the  development  of  the  convolutions  from  the  eighth  month 
onward.  The  male  is  said  to  have,  not  only  an  absolutely 
greater  cerebral  surface,  but  also  a  relatively  greater  growth 
of  the  parts  lying  in  front  of  the  central  fissure  as  compared 
with  those  lying  behind. 

Of  the  more  definitely  sexual  peculiarities  of  organism, 
both  stationary  and  periodic,  and  of  their  influence  on  the 


AGE,    SEX,    AND   TEMPEKAMENT.  455 

general  physical  and  psychical  development,  it  is  unneces- 
sary to  speak. 

Mental  Differences  of  the  Sexes,  —  It  is  obvious  to  any 
candid  and  intelligent  observer  that  the  foregoing  differ- 
ences in  the  bodily  organism  of  the  male  and  female  involve 
most  profound  and  far-reaching  differences  in  the  mental 
life.  These  bodily  differences  chiefly  and  primarily  concern 
the  life  of  sensation,  emotion,  and  movement.  But  the 
mental  life  affected  is  fundamental  and  gives  conditions 
to  all  the  so-called  "  higher "  intellectual  and  spiritual 
faculties. 

The  superior  strength  of  the  chest,  shoulders,  and  hips 
of  the  male,  and  the  fitness  of  the  limbs  and  trunk  for  firm 
and  swift  movement,  give  him  a  superior  consciousness  of 
ease,  elasticity,  and  security ;  both  of  posture  and  in  changes 
of  position.  His  sensations  are  more  sharply  discerned  as 
respects  qualitative  content,  less  buried  under  the  feeling 
with  which  sensation  is  fused.  Decision,  self-control,  nicety 
and  definiteness  of  judgment,  as  connected  with  the  lower 
life  of  sensation  and  movement,  undoubtedly  belong  to  him 
in  superior  degree.  Even  more  important  sexual  differ- 
ences in  the  kind  and  amount  of  feeling  —  sensuous, 
sesthetical,  and  intellectual  —  are  connected  with  the  devel- 
opment of  the  organs  characteristic  of  sex.  The  female 
is  necessarily  more  under  the  control  of  feeling,  with  the 
exception  of  certain  of  the  coarse  appetites  and  passions ; 
she  is  more  subject  to  "  moods." 

The  differences  of  the  sexes  in  circulation,  respiration, 
and  metabolism,  are  connected  with  important  differences 
in  sentiment,  emotion,  and  other  forms  of  mental  life.  The 
female  can  better  endure  privation  of  air,  food,  and  exer- 
cise ;  she  is  more  patient  and  successful  in  the  passive 
bearing  of  pain.  But  the  larger  mass  of  nervous  matter, 
with  its  store  of  disposable  energy,  makes  the  male  much 
more  capable  of  all  pursuits  and  achievements  requiring 


456  PHYSIOLOGICAL  PSYCHOLOGY. 

such  energy.  And  since  all  scientific,  political,  commercial, 
and  nearly  all  artistic,  pursuits  and  achievements  require  — 
particularly,  and  with  increasing  imperativeness  in  these 
days  —  the  use  of  such  energy,  the  average  female  cannot 
compete  with  the  average  male  successfully  upon  this 
ground.  The  farther  we  advance  in  these  pursuits  and 
achievements,  the  more  determinative  does  the  constitu- 
tional difference  become.  It  is  undoubtedly  the  chief 
reason  for  the  difference — now  not  less  marked  than  ever 
—  between  the  two  sexes  in  the  higher  and  the  highest 
circles  of  such  endeavor  open  to  mankind. 

We  shall  touch  lightly  upon  the  much  disputed  point  of 
the  spiritual  characteristics  of  the  sexes.  Probably,  to  cite 
a  few  points  from  Lotze  will  sufficiently  represent  the  true 
state  of  the  case.  This  philosopher  holds  that  woman 
adapts  herself  more  easily  to  new  conditions  of  life  than 
does  man,  —  because  she  is  a  mixture  of  the  sanguine  tem- 
perament and  the  sentimental  stage  ;  while  varieties  of 
education  conceal  more  of  her  native  qualities.  It  is  char- 
acteristic of  masculine  philosophy  to  analyze  phenomena ; 
but  women  usually  hate  analysis.  Masculine  thought 
recognizes  that  what  is  great  and  beautiful  in  the  world 
has  its  fixed  mechanical  conditions  ;  masculine  effort  rever- 
ences general  principles.  The  faith  of  woman  is  that  the 
value  of  no  principle  is  independent  of  concrete  life ;  she 
is  devout  toward  sesthetical  completeness.  The  notions 
of  the  two  even  as  regards  spatial  and  mathematical  rela- 
tions are  markedly  different ;  the  same  thing  is  true  as  to 
their  perceptions  of  the  nature  of  the  concrete  realizations 
of  the  ideas  of  space  and  time. 

THE  THEORY  OF  TEMPERAMENTS. 

Few  impressions  are  more  firmly  fixed  than  this,  that 
different  individuals  (at  least  among  the  more  highly 
civilized  peoples)  are  possessed  of  different  natural  "  dis- 


AGE,    SEX,   AND   TEMPEEAMENT.  457 

positions."  The  term  "  natural "  expresses  the  current 
conviction  that  the  foundation  of  their  differences  is  innate 
and  inherited,  rather  than  the  result  of  training  and  envi- 
ronment. Experience  shows  that  a  so-called  "  disposition  " 
generally  maintains  itself  under  great  alterations  in  cir- 
cumstances, and  against  effort,  to  the  close  of  the  individ- 
ual's life.  Where  it  appears  to  be  greatly  modified,  such 
modification  is  usually  made  at  the  expense  of  greater 
energy  than  is  required  even  to  break  firmly  acquired 
habits.  Upon  such  patent  facts  the  theory  of  "  Tempera- 
ments "  is  based. 

Kinds  of  Temperament,  —  The  number  4  has  been  chosen 
most  often  to  express  the  fundamental  classes  of  tem- 
peraments. It  is  doubtless  true  that  this  number  cor- 
responds particularly  well  to  the  facts.  On  the  other 
hand,  no  strictly  scientific  induction  can  be  made,  either 
as  to  the  classification  of  temperaments,  or  as  to  the  physio- 
logical basis  upon  which  differences  of  temperament  rest. 
The  best  obtainable  treatment  of  the  subject  is,  therefore, 
a  mixture  of  keen  general  observation,  shrewd  conjecture, 
and  speculation  in  the  uncertain  realm  of  psycho-physical 
theory. 

A  writer  of  nearly  a  half  century  since  (Dr.  Leopold 
George)  would  define  the  four  temperaments  by  the  inte- 
rior relation  which  exists  between  perception  and  the 
affections  of  the  mind.  Thus,  for  example,  the  greater 
the  mind's  wakefulness  to  impressions,  the  greater  is  also 
its  susceptibility  to  the  feelings  of  pleasure  and  pain  which 
are  attached  to  the  impressions.  Hence  the  sanguine 
temperament,  which  is  distinguished  by  peculiar  strength 
in  this  interior  relation.  This  theory  is  extended  by  its 
author  so  as  to  apply  to  the  different  periods  of  life  and  to 
different  races  of  men. 

Modern  psychology  is  inclined  to  approach  the  subject  of 
temperament  from  the  physiological  and  biological  points 


458  PHYSIOLOGICAL  PSYCHOLOGY. 

of  view.  In  this  way  it  is  rendered  more  cautious :  it  can 
scarcely,  however,  be  said  to  have  added  much  to  the 
definiteness  of  our  verifiable  knowledge. 

Wundt's  Classification  of  Temperaments.  —  The  four-fold 
division  of  temperaments  is  adopted  by  this  writer  on  the 
ground  that,  in  every  individual,  there  must  be  a  certain 
combination  of  the  two  factors  of  strength  and  speed  in 
that  change  which  all  mental  processes  undergo.  The 
affections  of  the  mind  are  therefore  classifiable  as  either 
strong  and  quick,  or  strong  and  slow  ;  or  else  as  weak  and 
quick,  or  weak  and  slow.  By  crossing  these  two  principles 
of  division  the  following  scheme  is  derived  : 

Strong.  Weak. 

Quick "  Choleric  "     "  Sanguine." 

Slow "Melancholic" "Phlegmatic." 

The  quick  temperaments  are  directed  rather  toward  the 
present,  the  slow  toward  the  future.  The  quick  require 
additional  strength,  the  weak  additional  time,  in  order  to 
achieve  the  largest  amount  of  work  possible  for  them. 
The  choleric  and  phlegmatic  are  temperaments,  with 
respect  to  action ;  the  sanguine  and  melancholic  are  tem- 
peraments, with  respect  to  feeling. 

Wundt  adds  the  following  practical  suggestion  :  "  One 
should  be  sanguine  amid  the  petty  sufferings  and  joys  of 
daily  life,  melancholic  in  the  more  serious  hours  of  life's 
more  important  events,  choleric  toward  impressions  that 
fetter  one's  profounder  interests,  phlegmatic  in  the  execu- 
tion of  the  resolves  that  have  been  reached." 

Lotze's  Classification  of  Temperament.  —  By  the  term  "  tem- 
peraments "  Lotze  understands :  "  (1)  The  differences,  in 
kind  and  degree,  of  excitability  for  external  impressions; 
(2)  the  greater  or  less  extent  to  which  the  ideas  excited 
reproduce  others ;  (3)  the  rapidity  with  which  the  ideas 
vary  ;  (4)  the  strength  with  which  feelings  of  pleasure  and 


AGE,   SEX,   AND   TEMPERAMENT.  459 

pain  are  associated  with  the  ideas ;  (5)  finally,  the  ease 
with  which  external  actions  associate  with  these  inner 
states  themselves."  This  authority  also  adopts  the  four- 
fold division  of  temperaments. 

The  sanguine  temperament  Lotze  holds  to  be  distin- 
guished by  great  rapidity  of  change  and  lively  excitability. 
It  indicates  an  excess  of  sensitiveness  to  all  external  stim- 
uli, and  of  capacity  for  reciprocal  excitement  among  the 
different  psychical  states.  For  the  temperament  usually 
called  "  melancholic  "  he  would  substitute  the  term  sen- 
timental. This  temperament  is  distinguished  "  by  special 
receptivity  for  the  feeling  of  the  value  of  all  possible  rela- 
tions " ;  but  is  indifferent  toward  bare  matter  of  fact.  It 
implies  a  lively  appreciation  of  harmony  and  discord,  great 
variety  of  sesthetical  feeling  and  imaginative  activity,  — 
often  with  theoretical  vagueness,  ready  yielding  of  the 
sense  of  duty  to  inclination,  and  dislike  of  hard  work. 

The  choleric  temperament  is  marked  by  "  one-sided  recep- 
tivity and  great  energy  in  single  directions."  It  implies 
diminished  susceptibility  to  excitement,  but  increased  force 
and  endurance  in  reaction  when  once  the  feeling  has  been 
aroused.  Its  best  effect  is  steadiness  of  character ;  but  its 
uncomely  effect  may  be  an  obstinate  and  narrow  persever- 
ance in  a  path  once  entered  upon,  even  when  reasons  exist 
for  deviating  from  or  abandoning  it.  Finally,  the  phleg- 
matic temperament  is  distinguished  by  slightly  varied  and 
slow,  but  not  necessarily  weak,  reactions. 

Physical  Basis  of  Temperament.  —  Nothing  definite  is 
known  as  to  the  physiological  grounds  on  which  rests 
the  distinction  of  temperaments.  The  influence  of  abnor- 
mal bodily  conditions,  and  of  certain  diseases,  to  produce 
or  alter  the  disposition  in  a  manner  resembling  tempera- 
ment would  seem  to  indicate  that  the  original  constitution 
of  the  brain  is  not  the  primary  determining  factor.  The 
susceptibility  of  the  end-organs  of  sense  to  external  stimuli, 


460  PHYSIOLOGICAL  PSYCHOLOGY. 

and  the  strength  of  the  resulting  reactions  in  the  form  of 
common  feeling,  as  well  as  the  constitution  of  the  visceral 
organs  and  the  coloring  they  impart  to  every  form  of  feel- 
ing, appear  to  be  of  prime  importance. 

Many  authorities,  not  without  a  show  of  reasons,  assign 
the  different  temperaments  to  the  four  main  periods  of  life 
as  distinctive  of  them, — the  sanguine  of  childhood,  the 
sentimental  of  youth,  the  choleric  of  maturity,  the  phleg- 
matic of  old  age.  The  fact  that  different  periods  of  life 
are  apt  to  be  characterized  by  a  predominance  of  one  of  the 
four  temperaments  is  not  an  argument  against  the  physi- 
cal nature  of  the  basis  of  temperament.  For  changes  in 
the  nature,  speed,  and  strength  of  the  reactions  derived 
from  the  end-organs,  and  from  the  internal  organs  of  the 
trunk,  necessarily  accompany  the  early  development,  the 
maturing,  and  the  decay  of  the  bodily  powers.  These 
things  cannot  fail,  of  course,  to  have  a  great  though  indi- 
rect influence  upon  the  cerebral  centres. 

Characteristics  of  Different  Races.  —  The  theory  of  tem- 
peraments has  been  applied  to  different  peoples,  with  more 
or  less  of  success.  For  example,  Dr.  George  would  char- 
acterize the  French  as  sanguine,  the  English  as  melan- 
cholic, the  Spanish  and  Italians  as  choleric,  the  Germans 
as  phlegmatic.  More  generally  still,  the  Caucasian  race 
is  sanguine ;  the  Mongolian  melancholic ;  the  Negro  phleg- 
matic ;  the  Malayan  choleric.  There  seems  little  doubt 
that  temperamental  characteristics  are  more  marked  among 
the  civilized  races  ;  if,  indeed,  they  exist  at  all  in  any  true 
sense  of  the  word,  among  the  savage  and  lower  uncivilized 
races.  It  must  be  acknowledged,  moreover,  that  the  whole 
matter  of  such  an  application  of  the  theory  does  not  admit 
of  a  strictly  scientific  discussion  and  presentation. 

In  the  more  obvious  external  characteristics  the  differ- 
ent races  of  men  vary  greatly.  Such  characteristics  are 
influenced,  to  a  considerable  but  unknown  extent,  by  soil, 


AGE,    SEX,   AND   TEMPERAMENT.  461 

climate,  food-supply,  and  prevalent  manner  of  living ;  but 
they  are  developed  under  the  general  laws  of  heredity 
and  variability  as  applied  to  the  particular  case  of  man. 
It  is  in  the  special  features  of  height,  weight,  and  relative 
form  rather  than  size  of  the  organs,  that  these  character- 
istic differences  chiefly  consist.  "  The  real  differences 
which  the  races  present,"  says  an  authority  on  this  subject 
(Quetelet),  "  appertain  to  characteristics  which  the  eye 
seizes  better  than  the  compasses ;  in  order  to  establish 
them  firmly,  an  appreciation  of  minute  differences  is  re- 
quired, and  a  tact  that  presupposes  a  long  experience  in 
such  researches.  One  can  see  the  difficulties  with  which 
phrenologists  meet  in  making  numerical  estimates  of  the 
characteristics  of  the  skull;  nothing  precise  can  be  for- 
mulated in  this  regard." 

Upon  the  general  subject  of  individual  and  race  charac- 
istics  it  remains  only  to  add  that  "  pure  "  cases  of  any  of 
the  four  or  more  recognized  varieties  of  temperament  are 
comparatively  rare.  Here,  as  in  other  similar  subjects,  the 
lines  which  science  attempts  to  draw  are,  in  nature,  crossed 
and  confused.  Mixed  temperaments  abound  among  the 
individuals  of  any  civilized  people ;  and  no  race  exists 
that  does  not  contain  all  kinds  of  temperaments  and  so 
overlap,  as  it  were,  the  boundaries  of  all  the  other  races 
—  even  those  from  which  its  average  is  most  widely 
separated. 


CHARTER  XIX. 

CONNECTION  OF  BODY  AND  MIND. 

WE  have  thus  far  been  studying  certain  groups  of  rela- 
tions which  exist  between  the  structure  and  activity  of  the 
nervous  mechanism  and  the  phenomena  called  "  mental," 
or  phenomena  of  "consciousness."  These  relations  may 
be  summarized,  with  a  fair  amount  of  accuracy  and  com- 
pleteness, under  the  following  five  heads. 

1.  The  quality  and  intensity  of  the  sense-element  in  our 
experience  is  related  to  the  condition  of  the  nervous  system 
as  acted  on  by  its  appropriate  stimuli.  The  true  state  of 
the  case  with  respect  to  these  relations  is,  indeed,  never  to 
be  represented  by  considering  this  sense-element  as  though 
it  consisted  merely  of  passive  impressions  dependent  upon 
the  kind  and  degree  of  the  action  which  the  stimuli  exert. 
The  same  element  is  also  dependent  upon  the  habits  and 
the  present  condition  of  the  mind,  at  the  time  the  stimulat- 
ing effect  of  the  excited  sensorium  is  realized  in  conscious- 
ness. Mental  habits  and  mental  condition  are,  in  turn, 
related  to  the  "  dynamical  associations  "  and  present  occu- 
pation, as  it  were,  of  the  cerebral  centres  at  the  time  when 
the  mental  phenomena  occur. 

The  entire  sense-element  —  the  various  kinds  and  degrees 
of  sensations  —  is  a  f orthputting,  a  characteristic  mode  of 
the  reaction,  of  the  mind.  Moreover,  many  of  the  phenom- 
ena which  belong  under  this  group  of  relations,  and  espe- 
cially the  marked  effect  of  attention  upon  the  sense-element 
itself,  prevent  us  from  regarding  the  relations  as  simple  and 
one-sided.  The  mental  state  which  is  apparently  most 

462 


CONNECTION   OF   BODY   AND   MIND.  463 

simple  and  passive  is  really  a  complex  and  characteristic 
activity  of  the  subject  of  all  mental  states,  —  namely,  of 
the  mind. 

2.  The  synthesis  of  our  conscious  experiences  is  related  to 
the  combination  in  the  cerebral  centres  of  the  impressions, 
made  from  whatever   source,    upon   the   nervous    organism. 
That  the  number,  form,  order,  and  time-rate  of  our  mental 
states  depend  upon  the  number,  kind,  order,  and  time-rate 
of  the   separate    excitations  which   are    combined  in  the 
centres  of  the  brain,  there  can  be  no  doubt.     At  the  same 
time,  no  mechanical  mixture  or  fusion  of  these  excitations, 
within  common  or  allied  areas  of  nervous  substance,  in  the 
least  degree  resembles  that  mental  synthesis  which  expe- 
rience implies.     An  activity  that  combines  under  different 
laws  from  those  which  govern  the  various  nerve-commo- 
tions, as  they  are  excited  in  the  brain  by  external  and 
internal  stimuli,  must  take  place  in  order  that  one  object 
may  be  cognized  by  one  subject,  —  the  cognizing  mind. 

3.  Those    phenomena    of    consciousness    which    we    call 
"memory"  and  "recollection"  imply  relations  with  the  estab- 
lished molecular  constitution  and  tendencies  of  the  cerebral 
centres.     But  the  peculiarly  mental  phenomena,  which  we 
call  by  these  terms,  bear  no  resemblance  to  those  which, 
so  far  as  we  know  or  conjecture  them,  are  called  by  such 
terms  as  "  organic  memory,"  "  dynamical  associations,"  etc. 
Especially  is  it  true  of  conscious  recognition,  — involving, 
as  it  does,  the  conscious  appropriation  of  the  present  men- 
tal state,  as  representative  of   another  past  state,  to  the 
same  one  subject  to  whom,  as  its  states,  both  that  which 
represents  and  that  which  is  represented  belong,  —  that 
this  is  a  something  utterly  unimaginable  and  inexplicable 
in  terms  of  revived  nerve-waves  or  molecular  agitations 
of  a  nervous  mass. 

4.  The  course  of  the  ideas,  and  the  changing  tone  of  feeling 
and  emotion,  are  related  to  the  vital  conditions  of  the  cere- 


464  PHYSIOLOGICAL   PSYCHOLOGY. 

bral  centres.  But  here  again,  mingling  with  all  these 
changing  mental  phenomena,  we  find  what  is  known  in 
consciousness  as  self-control.  iSelf-contiol  is  an  immediate 
determination  of  the  states  of  consciousness,  and  through 
them  a  determination  of  the  states  of  the  "  body,"  which 
is  to  be  attributed  to  the  conscious  mind  as  its  origin  or 
source.  To  speak  of  this  unique  experience  as  though 
the  science  of  physiological  psychology  had  disproved  its 
reality,  or  had  shown  it  actually  to  be  other  than  what  it 
obviously  appears  in  consciousness  as  being,  is  absolutely 
without  any  sufficient  warrant.  To  call  this  unique  experi- 
ence an  "illusion"  is  to  do  violence  to  the  science  of 
psychology  in  behalf  of  conjectures  attached,  but  not 
belonging,  as  verified  facts  or  principles,  to  the  allied  sci- 
ence of  physiology. 

5.  The  inherited  peculiarities  (tribal,  family,  and  sexual) 
of  the  organism  are  related  to  the  general  tone  or  coloring  of 
all  the  conscious  mental  life.  That  differences  of  disposi- 
tion and  temperament  exist,  which  are  innate  and  perma- 
nent, and  that  these  differences  are  dependent  upon  the 
inherited  bodily  constitution,  there  is  no  reasonable  ground 
to  dispute.  On  the  other  hand,  we  cannot  adopt  that  fan- 
ciful philosophy  which  considers  the  mind  as  the  builder 
of  the  body  —  as  in  some  direct  way  fashioning  to  its  own 
inherent  constitution  and  uses  the  organs  of  the  physical 
mechanism.  But  the  popular  impression  that  the  mind 
"  influences  "  the  body,  and  has  even,  within  certain  limits, 
the  power  of  shaping  it  to  its  needs,  and  of  profoundly 
modifying  its  molecular  structure  and  action,  has  ample 
warrant  in  the  facts. 

In  explanation  and  justification  of  the  popular  impres- 
sion we  shall  now  speak  further  upon  this  point.  The 
popular  impression,  as  expressed  in  the  popular  language, 
is  obviously  based  upon  the  assumption  that  some  kind  of 
reality  exists  which  corresponds  to  the  term  "  the  mind." 


CONNECTION   OF   BODY   AND   MIND.  465 

This  reality  stands  —  it  is  further  assumed  —  in  real  con- 
nections with  a  reality  of  another  kind,  —  namely,  with 
the  body.  The  nature  of  these  connections  is  vaguely 
and  figuratively  (always  figuratively)  expressed  by  various 
phrases  and  words.  Thus,  the  body  is  frequently  spoken 
of  as  the  "  seat  "  or  "  organ  "  of  the  mind.  The  one  party, 
in  this  fancied  dual  partnership,  is  said  to  "  influence  "  or 
"  control "  the  action  of  the  other.  Sometimes,  but  usu- 
ally not  in  the  language  of  the  people,  the  phenomena  of 
consciousness  are  regarded  as  "  products,"  or  "  resultants," 
or  "  manifestations,"  of  the  functional  activity  of  the  brain. 
That  some  kind  of  "  bond,"  or  "  tie,"  or  "  connection," 
exists  between  body  and  mind,  few  are  found  bold  enough 
to  doubt. 

What  that  is  true  to  the  facts  of  physiological  psychol- 
ogy, and  also  defensible  by  that  branch  of  philosophy 
which  concerns  itself  with  what  men  call  "  real,"  is  signi- 
fied by  such  popular  expressions  as  these  ? 

The  Body  as  the  "  Seat  "  of  the  Mind,  —  The  mind  is  com- 
monly regarded  as  connected  with  the  body  by  being  in 
the  body.  This  general  assumption  that,  in  some  sense, 
the  mind  is  in  the  body  is  yet  more  figuratively  expressed 
by  saying :  The  body  is  the  "  seat "  of  the  mind.  It  is 
not  plain  at  once,  however,  just  what  is  meant  by  this 
figure  of  speech. 

Experience  undoubtedly  justifies  the  popular  language 
in  regarding  the  mind  as  "  in  "  the  body,  in  the  same  sense 
of  the  words  which  warrants  us  in  also  saying :  it  is  not 
in  yonder  bird,  or  star,  or  tree.  Hence,  certain  now  anti- 
quated forms  of  philosophy  represented  perception  as 
though  it  were  a  process  in  which  the  mind  streams  out 
through  the  avenues  of  sense  and  thus  embraces  the  object 
of  sensuous  perception.  Others  thought  of  some  image 
or  etherealized  copy, of  the  object  as  streaming  into  the 
mind  through  the  same  avenues  of  sense.  The  modern 


466  PHYSIOLOGICAL   PSYCHOLOGY. 

study  of  perception,  on  a  basis  of  experiment  and  analysis, 
has  disproved  these  and  all  similar  ways  of  regarding  the 
relations  of  the  mind  to  external  things. 

The  ancients  located  the  soul  in  the  heart  or  the  lower 
viscera,  because  of  certain  obvious  relations  between  men- 
tal states  and  the  conditions  of  these  organs.  The  more 
obvious  relations,  however,  were  for  the  most  part  con- 
fined to  the  emotional  states  of  the  soul.  We  have  seen 
that  they  had  little  suspicion  of  the  intimate  and  extensive 
dependence  of  the  mental  life  upon  the  constitution  and 
functional  activity  of  the  contents  of  the  skull.  Modern 
science,  with  a  sufficient  array  of  evidence,  emphasizes  the 
dependence  of  mental  life  upon  the  brain. 

In  whatever  sense,  then,  the  mind  can  be  said  to  be 
really  "  in  "  the  body,  in  that  sense  must  it  be  said  to  be 
really  "  in  "  the  brain.  But  what  that  is  real  do  we  mean 
by  speaking  of  the  mind  as  having  its  seat  within  the 
brain  ? 

Our  present  physiological  and  anatomical  knowledge  of 
the  human  cerebrum  and  its  functions  is  unfavorable  to  a 
view  which  would  "  seat "  the  mind  in  any  single  and 
limited  locality  of  this  organ.  Descartes,  indeed,  found  in 
the  pineal  gland  the  special  seat  of  the  soul.  We  know  of 
no  special  significance  which  this  small  bit  of  nervous  sub- 
stance possesses.  The  modern  science  of  the  localization 
of  cerebral  function  has  changed  our  entire  way  of  consid- 
ering the  matter.  In  whatever  sense  the  mind  has  its 
"seat"  in  any  part  of  the  body,  in  that  same  sense  it  has 
various  seats  for  its  various  related  activities.  And  yet 
the  unity  of  the  mind  in  consciousness  —  the  thing  which, 
above  all  others,  the  investigations  of  physiological  psychol- 
ogy are  powerless  to  explain  —  is  not  at  all  affected  by 
this  variety  of  local  relations  between  itself  and  the  cen- 
tres of  the  brain. 

An  analysis  of  the  popular  language,  in  connection  with 


CONNECTION   OF   BODY   AND   MIND.  467 

the  facts  and  theory  examined  in  Chapters  XIII.-XIV., 
shows  us  what  its  real  meaning  is.  The  phenomena  of 
sensation-complexes  that  are  localized  and  projected  as  the 
different  areas  of  our  own  body,  and  the  phenomena  that, 
being  tinged  with  feelings  of  pleasure  and  pain,  are  most 
obviously  ascribed  to  our  own  soul  as  it  states,  are  con- 
stantly interrelated  in  experience.  But  man  is  a  meta- 
physical being.  He  naturally  and  necessarily  assumes 
"  real "  existences  as  the  subjects  of  these  two  markedly 
different  classes  of  occurrences.  The  localized  and  pro- 
jected sensation-complexes  are  attributed  to  one  reality,  — 
to  a  material  body ;  the  experiences  that  have  an  interest, 
because  they  are  so  suffused  with  feeling,  are,  in  a  pecul- 
iar way,  assigned  to  another  real  being,  to  a  "  Self  "  or  a 
soul.  How  this  "  diremption  "  of  experience  comes  about, 
so  far  as  the  history  of  the  process  can  be  traced  and 
explained,  it  is  foreign  to  our  present  purpose  further  to 
inquire. 

It  is  then  a  genuine  metaphysical  activity  of  the  mind 
which  is  testified  to,  whenever  the  popular  language  speaks 
of  the  body  as  the  "  seat "  of  the  soul.  And  the  kind  of 
experience  which  fosters  and  supports  this  metaphysical 
activity  is  the  experience  of  localizing  and  projecting,  in  a 
systematic  way,  certain  of  our  own  sensation-complexes. 

But  what  is  meant  when,  in  the  name  of  modern 
science,  we  limit  that  part  of  the  body,  in  which  the  soul 
has  its  "  seat,"  to  the  higher  nervous  centres  ?  The  meta- 
physics of  this  process  is  essentially  the  same  as  that 
expressed  in  the  popular  language.  But  the  kind  of 
experience  on  which  the  metaphysical  assumption  rests  is 
much  more  remote  from  our  daily  life.  Its  observations 
demand  rare  and  refined  instrumentalities ;  its  conclusions 
rest  upon  complicated  and  often  doubtful  inferences. 

Unless,  however,  we  are  ready  to  deny  all  reality  to  the 
assumptions  and  affirmations  of  both  popular  language  and 


468  PHYSIOLOGICAL   PSYCHOLOGY. 

modern  scientific  researches,  they  mean  essentially  the 
same  thing.  Neither  means  that  an  entity  called  "  soul  " 
is  suffused  through  another  entity  called  "  body,"  as 
luminiferous  ether  may  be  supposed  to  interpenetrate  the 
substance  of  the  window-pane.  Neither  means  that  an 
entity  called  soul  maintains  a  "  sitting  "  or  other  sort  of 
posture,  whether  in  the  peripheral  or  in  the  cerebral  areas 
of  the  entity  called  body.  But  both  forms  of  expression 
assume  the  existence,  in  reality,  of  both  a  body  and  a 
soul.  Both  affirm  that  these  two  existences  are,  for 
certain  of  their  activities,  interdependent. 

Body  as  the  "  Organ  "  of  Mind,  —  Another  set  of  relations, 
which  are  customarily  assumed  to  exist  in  reality  between 
the  body  and  the  mind,  is  expressed  by  such  words  as 
"  organ  "  or  "  instrument."  These  terms  are  intended  to 
emphasize  the  connection,  in  reality,  between  the  ideas  and 
volitions  which  arise  in  consciousness,  and  the  induced 
movements  of  the  muscular  apparatus.  But  the  term,  as 
popularly  employed,  is  plainly  figurative  to  a  high  degree. 
An  instrument,  or  organ,  is  any  material  medium  between 
the  masses  of  matter,  whose  shape  or  position  we  wish  to 
change,  and  the  movable  parts  of  our  own  bodies.  Or  it 
is  a  means  of  sharpening,  defining,  and  multiplying  our 
sensations  and  perceptions  of  things.  Or,  again,  it  is  an 
apparatus,  by  producing  changes  in  which,  we  express 
sentiments  and  ideas.  With  the  instruments  of  spade  and 
shovel  we  throw  up  the  ground;  with  pulley  and  lever 
we  raise  weights.  With  microscope  or  telescope,  as  organs 
added  to  the  natural  organ  of  the  eye,  we  see  things  minute 
and  near,  or  larger  and  far  remote.  With  that  instrument, 
whose  name  is  "  organ,"  we  express  our  musical  sentiments 
and  ideas. 

Few  persons,  however,  will  be  found  so  crude  in  concep- 
tion as  to  suppose  that,  in  reality,  when  a  limb  is  moved, 
an  entity  of  some  kind,  called  "  mind,"  is  laying  some  sort 


CONNECTION   OF   BODY   AND   MIND.  469 

of  material  clutch  —  present  there  —  upon  the  muscular 
fibre.  Certainly  no  one,  well  informed  enough  to  know 
of  the  existence  and  character  of  cerebral  localization, 
supposes  that  this  same  entity  plays,  in  a  physical  way, 
upon  the  nerve-eells  and  fibres  of  the  cerebral  centres. 

But  every  form  of  conception,  whether  popular  or  scien- 
tific, which  leads  to  the  use  of  words  like  "  instrument "  or 
"  organ  "  in  the  effort  to  express  essential  relations  of  body 
and  mind,  implies  the  same  experience,  and  sets  forth  the 
same  truths.  There  are  two  realities  implied,  —  the  body 
and  the  mind;  and  these  two  are,  in  reality,  interdepen- 
dently  connected. 

The  Word  "  Connection  "  as  applied  to  Body  and  Mind.  — 
Much  of  the  popular  language  undoubtedly  implies  that 
some  "  bond  "  exists  between  the  body  and  the  mind.  "In 
summing  up  the  results  of  our  previous  researches  we  have 
frequently  felt  ourselves  obliged  to  use  the  term  "  connec- 
tion." Both  these  terms,  however,  like  the  ones  already 
examined,  are  plainly  of  a  figurative  character.  Of  course 
—  it  needs  no  argument  to  show  this  —  no  actual  bond  or 
tie,  such  as  we  employ  to  make  two  material  things  act  in 
certain  desired  relations,  whenever  they  do  not  "  naturally  " 
so  act,  unites  the  body  and  the  mind.  But  the  essential 
truth  is  this :  In  the  order  of  nature,  the  body  and  mind 
do  naturally  act  under  binding  relations  toward  each  other. 
Body  and  mind  behave  with  reference  to  each  other,  as 
though  bound. 

Yet  again,  we  cannot  speak  of  any  one  bond  or  connec- 
tion as  existing  between  those  two  beings  which  we  desig- 
nate by  the  words,  body  and  mind.  No  single  formula  can 
express  all  the  various  natural  forms  of  their  related 
behavior.  The  whole  investigation  of  physiological  psy- 
chology aims  to  discover  as  many  as  possible  of  those 
natural  forms  of  relation,  of  those  so-called  "  bonds "  or 
"connections,"  which  exist  between  the  two.  It  traces 


470  PHYSIOLOGICAL   PSYCHOLOGY. 

inward  and  backward,  the  obvious  changes  in  the  periphery 
of  the  body,  until  it  finds  them  resulting  in  molecular 
changes  of  mysterious  chemical,  thermic,  nutritive,  and 
distinctively  nervous,  orders,  within  the  substance  of  the 
brain.  With  these  molecular  changes  it  "  connects  "  the 
concurrent  or  subsequent  mental  phenomena.  But  such 
connection  is  no  physical  tie  or  bond.  By  the  word  "  con- 
nection," we  only  signify  the  ultimate  fact  that  the  two 
beings,  which  are  the  subjects  of  the  two  classes  of  changes, 
are  in  the  order  of  nature  causally  related. 

If  it  should  be  complained  that,  in  this  way,  the  entire 
investigation  of  physiological  psychology  ends  in  a  mys- 
tery, the  truth  of  the  complaint  must  be  granted.  The 
fact  that  body  and  mind  are  thus,  in  a  great  variety  of  par- 
ticular ways,  causally  related,  is  an  ultimate  fact ;  —  this,  so 
(  far  as  science,  with  its  legitimate  inferences,  can  go.  But 
all  so-called  causal  relation  is  equally  mysterious;  it  all 
partakes  of  the  nature  of  ultimate  and  inexplicable  fact. 
That  one  atom  of  oxygen  should  influence,  or  cause, 
another  to  act  in  a  certain  way,  is  also  an  ultimate  myste- 
rious fact.  That  an  atom  of  oxygen  should  cause  other 
atoms  of  hydrogen,  carbon,  nitrogen,  etc.,  to  act  in  a  great 
variety  of  different  ways,  involves  numerous  equally  mys- 
terious and  ultimate  "  connections." 

Exertion  of  Energy  between  Body  and  Mind,  —  Modern 
physics  has  established  an  important  principle,  called  the 
"conservation  and  correlation  of  energy."  Closely  con- 
nected with  this  principle  (indeed  the  same  thing  as  one 
side  of  this  principle),  is  the  assumption  that  the  quantum 
of  physical  energy  in  the  universe  is  invariable.  These 
principles  modern  biology  has  borrowed  from  modern  phys- 
ics. Strictly  speaking,  however,  it  is  only  within  com- 
paratively narrow  lines  of  even  physical  researches  that 
the  principle  of  the  conservation  and  correlation  of  energy 
can  be  inductively  established.  And  chemistry  would 


CONNECTION   OF  BODY   AND   MIND.  471 

make  few  indeed  of  its  present  splendid  advances  if  it 
were  confined  to  deductive  predictions,  under  this  prin- 
ciple, concerning  the  behavior  of  molecules  and  atoms  in 
their  various  relations.  In  spite  of  all  its  serious  attempts, 
biology,  too,  is  far  enough  from  the  position  in  which  it 
can  make  much  use  of  the  same  principle. 

Few  will  question  the  statement  that  any  so-called  in- 
fluence, or  causal  action,  of  body  and  mind  upon  each 
other,  is  incapable  of  expression  in  terms  of  the  conserva- 
tion and  correlation  of  physical  energy.  Energy,  whether 
stored  or  kinetic,  within  the  nerve-cells  of  the  cerebral 
centres  cannot  become  stored  or  kinetic  in  the  assumed 
subject  of  mental  phenomena.  And,  really,  although  we 
use  terms  of  quantity  to  describe  mental  phenomena,  they 
cannot,  as  mental,  be  correlated  under  this  great  physical 
principle  with  quantities  of  the  molecular  changes  that 
occur  in  the  brain.  No  mental  energy  ever  passes  over 
into  the  brain ;  no  nervous  energy  ever  passes  over  into 
the  mind.  Indeed,  the  very  attempt  to  apply  the  concep- 
tions and  terms,  so  familiar  to  physics  and  so  scientific 
when  dealing  with  the  relations  of  physical  masses  and 
movements,  ends  in  palpable  absurdities  when  the  subject 
of  treatment  becomes  the  relations  of  body  and  mind. 

In  view  of  these  and  other  similar  difficulties,  some 
would  utterly  refuse  to  speak  of  body  arid  mind  as,  in  any 
true  sense  of  the  word,  causally  interrelated.  But  such  a 
refusal  leaves  all  popular  and  all  scientific  language  with- 
out any  ground  in  reality  on  which  to  stand.  We  are 
obliged  to  talk  as  though  the  mind  behaves  thus  and  so, 
"  because  "  of  the  simultaneous  or  previous  behavior  of  the 
body,  to  which  it  naturally  stands  in  relations.  With 
equal  confidence  do  we,  in  both  ordinary  and  scientific 
terms,  assert  the  causal  action  of  the  mind  upon  the  body. 
There  is  as  much  valid  reason  for  all  this  as  there  is  for 
regarding  any  two  sets  of  phenomena,  and  any  two  beings 


472  PHYSIOLOGICAL   PSYCHOLOGY. 

considered  as  the  subjects  of  the  phenomena,  as  standing 
in  causal  relations.  There  is  as  much  reason  for  saying 
that  my  volition  causes  my  limbs  to  move,  and  that  the 
light-waves  on  the  retina  cause  in  me  sensations  and  per- 
ceptions, as  there  is  for  saying  that  the  earth  causes  the 
meteor  to  fall  to  its  surface,  or  the  sun  causes  the  plant  to 
grow  by  its  warmth  and  light. 

Mind  and  Body  in  Causal  Relations.  —  We  are  therefore 
warranted  in  maintaining  that  the  changes  of  the  human 
brain  and  the  phenomena  of  human  consciousness  stand 
toward  each  other  in  the  relation  of  cause  and  effect.  The 
general  relation  of  cause  and  effect  is  far  more  profound 
and  extensive  in  its  application  than  the  modern  physical 
postulate  of  the  conservation  and  correlation  of  energy. 
The  relation  of  cause  and  effect  is,  indeed,  the  ultimate 
fact  —  itself  inexplicable  —  by  the  various  applications  of 
which  we  "  explain "  all  events  in  the  world  of  matter 
and  of  mind.  But  the  principle  of  the  conservation  and 
correlation  of  energy  is  only  a  valid  and  useful  working 
hypothesis  under  which  we  may  bring  certain  classes  of 
physical  phenomena. 

When,  then,  we  attempt  to  consider  the  relation  of  the 
brain  and  the  mind  without  using  terms  of  causation,  we 
find  ourselves  landed  in  unreason  through  the  effort  to 
escape  a  fundamental  law  of  all  reason.  But  when  we 
attempt  to  apply  the  physical  formula  (the  principle  of 
the  conservation  and  correlation  of  energy)  to  the  case 
of  brain  and  mind,  we  find  ourselves  landed  in  absurdities 
of  a  practical  as  well  as  of  a  scientific  sort.  All  the  re- 
searches of  physiological  psychology  imply  that  changes 
in  the  material  organism  and  changing  mental  states  are 
causally  connected.  All  its  discoveries  are  designed  to 
render  more  precise,  and  to  reduce  to  as  nearly  exact  terms 
as  possible,  the  statements  of  these  causal  relations.  On 
the  other  hand,  all  its  discoveries  emphasize  the  complete 


CONNECTION   OF   BODY   AND   MIND.  473 

impossibility  of  considering  these  causal  relations  in  terms 
of  the  conservation  and  correlation  of  physical  energy. 

It  may  be  said  again  that,  in  the  last  analysis,  the  fore- 
going conclusion  makes  it  impossible  for  science  to  com- 
prehend the  connection  of  body  and  mind.  All  that  we 
call  the  "  science  "  of  their  relations  rests  back  upon  an 
ultimate  fact.  This  is  true  —  as  true  and  mysterious  — 
of  the  subjects  with  which  physiological  psychology  deals 
as  of  those  considered  by  other  forms  of  science. 

But  what  is  there  in  the  nature  of  the  so-called  "  causal 
nexus"  which  should  prevent  its  being  assumed  to  exist 
between  the  body  and  the  mind  ?  In  reply,  we  might  ask : 
What  do  we  really  mean  when  we  speak  of  an  event,  or 
a  thing,  as  the  "  cause  "  of  another  ?  What  do  we  mean 
when  we  speak  of  "  exerting  influence,"  or  of  "  acting 
and  being  acted  upon,"  as  between  two  beings  in  the 
world  of  manifold  existences?  Nothing  that  the  senses 
can  discover,  or  the  imagination  depict  in  terms  of  sense. 
Such  affirmations  are  born  of  reason ;  they  arise  from  a 
postulate  of  the  higher  activity  of  the  mind  itself.  They 
express  in  various  modifications,  the  ultimate,  mysterious 
fact  of  a  relation,  in  reality,  between  those  beings  whose 
states  are  observed  to  be  correlated  with  each  other  under 
uniform  laws.  And  that  this  fact  of  causal  relation 
maintains  itself  with  reference  to  body  and  mind,  there 
are  the  most  abundant  reasons  to  affirm  rather  than  to 
deny. 

Causal  Influence  of  the  Body  on  the  Mind.  —  Speaking 
naturally  and  without  prejudice,  no  one  would  hesitate  to 
regard  the  body  as  a  "  cause  "  of  the  phenomena  which 
we  attribute  to  the  subject  called  the  mind.  Who  doubts 
that  a  man  loses  his  senses,  as  truly  as  he  loses  a  portion 
of  his  brain-mass,  because  he  has  been  struck  a  blow  upon 
the  head  ?  The  stoppage  of  the  arteries  that  furnish  blood 
to  the  higher  cerebral  centres,  whether  by  outside  pressure 


474  PHYSIOLOGICAL  PSYCHOLOGY. 

or  by  embolism,  promptly  causes  the  disturbance  or  cessa- 
tion of  consciousness.  The  character  and  amount  of  blood 
circulating  in  these  centres  causes  marked  changes  in  the 
character  and  time-rate  of  mental  phenomena.  Witness 
the  effect  upon  the  mind  of  certain  drugs,  or  of  the  delir- 
ium of  fever.  Schroeder  van  der  Kolk  tells  of  a  patient 
who,  when  his  pulse  was  reduced  by  digitalis  to  50  or  60 
beats  per  minute,  was  mentally  quiet  or  depressed ;  when 
it  was  allowed  to  rise  to  90  beats,  his  mind  was  in  mani- 
acal confusion.  Cox  narrates  the  case  of  a  sick  man  who, 
at  40  pulsations  in  the  minute,  was  "  half-dead " ;  at  50, 
melancholic;  at  70,  quite  "beside  himself";  at  90,  "rav- 
ing mad."  Hallucinations,  not  infrequently,  immediately 
cease,  when  the  person  afflicted  with  them  assumes  the 
standing  posture,  or  has  leeches  applied  to  the  head. 

But  there  is  little  need  to  enumerate  facts,  at  this  stage 
of  our  investigations,  in  support  of  the  proposition  just 
made.  A  large  part  of  all  the  conclusions  of  which  the 
science  of  physiological  psychology  consists,  prove  noth- 
ing whatever,  if  they  do  not  prove  that  bodily  changes  are 
the  "causes"  of  alterations  in  mental  phenomena.  The 
chapters  on  the  localization  of  cerebral  function,  on  the 
quality  and  quantity  of  sensation,  etc.,  abound  in  facts  of 
the  order  required  for  such  proof. 

The  affirmation  of  a  causal  action  of  the  body  —  and 
more  especially  of  the  brain  —  upon  the  mind  does  not, 
however,  invalidate  the  claims  of  the  mind  to  be  con- 
sidered a  real  being,  or  to  be  spiritual  and  free.  For  the 
sole  account  or  cause  of  the  mind's  activities  can,  in  no 
instance,  be  found  in  the  molecular  condition  and  changes 
of  the  brain.  The  full  account  of  every  mental  state  must 
refer  directly  to  the  nature  of  that  subject,  the  mind  itself, 
of  which  it  is  the  state,  as  its  cause.  Even  the  simplest 
sensation  is  not  explained  solely  by  indicating  what  form 
of  nerve-commotion  in  the  cerebral  cortex  is  its  bodily 


CONNECTION   OF   BODY   AND   MIND.  475 

cause.  Every  sensation  must  also  be  considered  as  a  psy- 
chical activity  put  forth  by  the  being  called  mind.  There 
is  no  real  incompatibility  between  these  two  ways  of  re- 
garding every  mental  state.  Indeed,  every  change  of  state 
in  any  physical  being  demands  this  dual  way  of  regarding 
it.  Every  such  change  must  be  considered  both  as  caused 
by  a  change  of  states  in  other  beings  to  which  it  is  related, 
and  also  as  due  to  activity  of  that  being  to  which  as  a 
change  of  state,  it  belongs. 

Causal  Influence  of  the  Mind  upon  the  Body.  —  We  have  an 
equal  right,  however,  to  affirm  that  mental  states,  changes 
in  consciousness,  are  a  cause  of  changes  in  allied  cerebral 
centres,  and,  through  them,  in  the  other  tissues  and  organs 
of  the  body.  Speaking  naturally  and  without  prejudice, 
no  one  would  hesitate  to  regard  the  mind  as  causally 
influencing  the  condition  of  the  body.  /  Even  the  most 
purely  vegetative  of  the  bodily  processes  are  dependent  for 
their  character  upon  antecedent  states  of  the  mind.  It  is 
as  true  that  melancholy  causes  bad  digestion  as  it  is  that 
bad  digestion  causes  melancholy.  Care,  chagrin,  and 
ennui  poison  the  blood.  Excessive  voluntary  application 
and  over-excited  feeling  wear  away  the  brain.  The  most 
modern  researches  into  the  phenomena  of  hypnotism  lend 
evidence  to  the  view,  that  "  mental  suggestion  "  accounts 
for  the  abnormal  condition  and  action  of  the  cerebral 
centres  quite  as  truly  as  the  condition  of  these  centres 
accounts  for  the  strange  mental  phenomena  which  accom- 
pany this  complex  state  of  body  and  mind. 

The  entire  class  of  phenomena  which  we  are  entitled  to 
call  "voluntary"  might  be  appealed  to  in  proof  of  the  same 
principle.  Here  we  might  instance  the  voluntary  innerva- 
tion  of  an  organ  by  fixation  of  attention,  the  dependence 
of  reaction-time  upon  the  will  of  the  person  reacting,  the 
abstraction  of  regard  from  the  images  of  sense  when  occu- 
pied in  reflection,  as  well  as  all  the  more  marvellous  cases 


476  PHYSIOLOGICAL  PSYCHOLOGY. 

of  self-control  in  enduring  pain,  triumphing  over  disease, 
etc. 

The  elevation  of  the  bodily  activities  to  a  most  astonish- 
ing precision,  under  the  influence  of  high  and  strong  artis- 
tic feeling,  is  also  a  noteworthy  fact  of  the  same  order. 

It  appears,  therefore,  that  the  human  brain  is  a  vast 
collection  of  material  molecules,  whose  constitution  and 
arrangement  are  such  as  to  connect  them,  in  a  unique  way, 
with  certain  forms  of  external  physical  energy.  But  they 
are  also  capable  of  standing  in  yet  more  surprising  and 
unique  relations  to  a  being  of  a  different  nature  from  their 
own  —  that  is,  to  the  mind.  These  latter  relations  involve 
a  causal  connection  as  truly  as  do  relations  of  real  physical 
beings.  That  material  molecules  and  a  being  of  the  kind 
called  mind  can  be  causally  connected  is,  indeed,  a  myste- 
rious fact.  But  because  of  its  mystery,  it  is  no  less  to  be 
acknowledged  as  a  fact. 

Finally,  then,  the  assumption  that  the  mind  is  a  real 
being,  which  can  be  acted  upon  by  the  brain,  and  which  can 
act  on  the  body  through  the  brain,  is  the  only  one  compatible 
with  all  the  facts  of  experience. 

Processes  involved  in  the  Connection  of  Body  and  Mind.  — 
All  intercourse  between  material  objects  and  the  spiritual 
subject  we  call  "  Self  "  involves  three  processes.  Of  these 
one  is  physical,  the  other  physiological,  the  third  psychical. 
In  and  through  these  processes,  external  things  and  the 
subject  of  mental  states  mutually  condition  each  other. 

The  physical  process  consists  in  the  action  of  the  appro- 
priate modes  of  physical  energy  upon  the  end-organs  of 
sense.  These  modes  of  energy  are  brought  to  bear  upon 
the  nervous  portions  of  these  organs  by  means  of  mechan- 
ical contrivances  —  such  as,  for  example,  the  contrivances 
for  forming  an  image  upon  the  retina  of  the  eye,  or  for 
conveying  the  modified  acoustic  impulses  to  the  organ 
of  Corti  in  the  inner  ear.  With  this  kind  of  processes  the 


CONNECTION   OF   BODY  AND   MIND.  477 

science  of  physics — but  only  by  a  great  increase  in  the  re- 
finement of  its  methods  —  may  hope  to  deal  more  success- 
fully in  the  near  future. 

The  second  process  consists  in  transmuting  the  physical 
energy  into  a  physiological  process,  a  nerve-commotion 
within  the  nervous  system ;  and  in  propagating  this  nerve- 
commotion  along  the  proper  tracts  and  diffusing  it  over 
the  various  areas  of  the  brain.  It  belongs  to  the  science 
of  physiology  to  investigate  and  describe  this  process  and 
its  laws.  More  particularly,  the  science  of  this  process  is 
called  "  general  nerve-physiology,"  with  its  several  depart- 
ments of  more  highly  "  specialized  nerve-physiology." 

The  third  process  is  psychical ;  it  is  a  process  which  is  a 
psychical  event,  a  forthputting  of  the  peculiar  energy  of 
the  mind.  It  is  directly  correlated  with  the  physiological 
process  only  when  the  latter  has  been  realized  in  certain 
cerebral  areas.  The  psychical  process  cannot  be  explained 
wholly  as  a  resultant  of  the  cerebral  physiological  .process ; 
yet  it  is  an  activity  of  the  mind  which  is  conditioned  upon 
that  process.  When,  for  example,  the  particular  mental 
process  is  the  perception  of  some  "  external "  object,  it  is 
no  less  truly  a  psychical  process.  The  mind  creates  its 
own  objects ;  presents  itself  with  its  own  presentations  of 
sense;  acts  to  put  forth,  as  its  own  product,  that  which 
it  knows  as  "  not-itself ."  But  it  accomplishes  all  this  as 
dependent  upon  processes  that  take  place  in  other  beings, 
and  with  the  assumption  of  the  existence  of  such  beings, 
to  which  it  stands  in  relations  of  cause  and  effect. 


CHAPTER   XX. 
THE  NATURE   OF  MIND. 

THERE  can  be  no  doubt  that  the  popular  impression  is 
in  favor  of  affirming  the  reality,  unity,  and  spirituality  (or 
ft<m-materiality)  of  the  human  mind.  Indeed,  so  long  as 
we  take  only  the  populai  point  of  view  and  employ  only 
the  language  which  is  customary  to  it,  great  difficulty  is 
experienced  in  even  expressing  such  inquiries  as  the 
science  of  physiological  psychology  suggests.  It  is,  how- 
ever, the  scientific  study  of  those  phenomena  which  show 
a  special  dependence  of  mental  states  upon  nervous  condi- 
tions which  disturbs  the  popular  impression.  Does  science, 
then,  end  in  destroying  this  impression  ?  Or,  does  it  not, 
after  disturbing  and  modifying  it,  reinstate  it,  substan- 
tially unchanged,  upon  much  surer  and  more  defensible 
foundations  ? 

The  Question  as  to  the  Reality  of  Mind  stated.  —  Although 
the  general  confidence  of  men  in  the  reality  of  their  own 
minds  is  without  doubt,  there  is  no  more  obscure  and  puz- 
zling (question  than  this:  In  what  does  this  reality  con- 
sist ?  In  other  words :  What  is  it  to  be  real  as  all  men 
believe  their  mental  "  selves  "  to  be  real  ?  But  this  is  a 
question  which  it  belongs  to  the  metaphysics  of  mind,  as 
an  important  department  of  philosophy,  fully  to  discuss. 
As  such,  it  does  not  properly  belong  to  even  the  final  con- 
siderations of  physiological  psychology. 

There  is  a  form,  however,  in  which  the  debate  over  the 
reality  of  the  mind  may  properly  be  considered  as  con- 
nected with  the  subject  we  have  been  studying.  This 
478 


THE  NATURE  OF   MIND.  479 

form  is  proposed  under  the  heads  of  the  arguments  for  and 
against  what  is  called  the  "  materialistic  "  view  or  hypoth- 
esis. For  the  materialistic  view  of  mental  phenomena 
denies  the  popular  impression,  —  namely,  that  such  phe- 
nomena are  to  be  referred  to  the  mind  as  the  subject  or 
ground  of  them  all.  On  the  contrary,  it  affirms  that  the 
material  substance  of  the  living  and  active  nervous  system 
(especially,  or  wholly,  of  the  brain)  is  the  only  reality 
concerned  in  the  production  of  these  phenomena.  The 
mental  phenomena,  it  holds,  are  phenomenal  of,  manifesta- 
tions of,  the  only  "real  "  subject,  which  is  in  its  view  —  as 
we  have  already  said  —  not  mind,  but  the  wonderfully 
constituted  and  complex  system  of  material  molecules 
within  the  bony  cavity  of  the  skull. 

Is  this  view  which  we  have  called  "  materialistic  "  justi- 
fied by  the  facts  and  laws  of  physiological  psychology? 
Or  is,  on  the  contrary,  that  view  justified  which  regards 
the  mental  phenomena  as  rightly  assigned  to  a  real  being 
to  be  called  "  the  mind  " ;  and  yet  regards  this  real  being 
as  acting  in  causal  relations  with  the  material  substance 
of  the  brain  ? 

It  will  be  recalled  that  we  have  already  in  part  an- 
swered the  foregoing  questions  by  an  argument  against 
the  materialistic  view.  This  argument  will  now  be  re- 
sumed and  briefly  continued. 

Difference  between  Nerve-commotions  and  Mental  Phenom- 
ena, —  It  is  scarcely  necessary  to  urge  the  fact  that  states 
of  consciousness  are  not  identical  in  nature  with  molecular 
agitations  in  the  higher  centres  of  the  brain.  Not  even 
the  most  pronounced  materialists  would  venture  to  affirm 
their  identity.  Minute  movements,  or  chemical  and  vital 
changes,  in  the  molecules  of  the  cerebral  mass  differ  totally, 
as  phenomena,  from  states  of  sensation,  of  perception  and 
ideation,  with  their  accompanying  tones  of  pleasurable  or 
painful  feeling. 


480  PHYSIOLOGICAL  PSYCHOLOGY. 

Even  less,  perhaps,  would  any  one  think  of  identifying 
the  most  complicated  and  ample  nerve-commotions  with 
those  trains  of  thought  which  result  in  solving  a  mathe- 
matical problem,  or  with  those  feelings  of  adoration  and 
affection  which  some  men  experience  on  contemplating  the 
idea  of  God.  Mental  states,  on  the  one  hand,  are  known 
only  as  states  of  consciousness  that  are  mine;  but  states 
of  material  molecules  are  conjectured  as  changes  occurring 
in  my  brain.  The  complete  "  incomparability  "  of  these 
two  classes  of  phenomena  is  denied  by  none. 

Modern  science  tends  to  regard  all  physical  events  as 
modes  of  motion — alterations  in  the  relations  of  material 
atoms  or  masses  to  each  other  in  space.  This  is  as  true 
of  the  brain  of  the  philosopher  or  of  the  saint  as  it  is  of 
the  falling  meteor  or  the  upturned  clod  of  the  valley.  The 
very  assumption  which  underlies  materialism  —  namely, 
that  the  brain  is  an  extra-mental  and  material  being  which 
undergoes  changes  independent  of  all  mental  perception 
or  conception  of  these  changes  —  seems  to  involve  most 
unequivocally  the  incomparability  of  nerve-commotions 
and  mental  phenomena. 

Mental  States  not  "  Products"  of  the  Brain. —  In  the  effort 
to  substantiate  the  being  of  the  nervous  organism  and,  at 
the  same  time,  deny  that  of  the  mind,  various  terms  may 
be  employed  to  express  the  relation  between  the  two. 
Among  such  terms  the  word  "  product "  occurs.  We  hear 
it  said  that  the  brain  —  at  least  the  psycho-physical  centres 
— "  produces "  the  phenomena  of  consciousness.  It  is 
impossible,  however,  to  give  any  satisfactory  meaning  to 
the  word  "product"  in  a  connection  such  as  this.  By 
this  word  we  ordinarily  understand  the  new  form  into 
which  some  material  substance  is  shaped  by  the  action 
upon  it  of  some  piece  of  mechanism.  We  may,  indeed,  call 
certain  secretions  of  the  body  the  "  product "  of  the  tissues 
which  secrete  them,  in  somewhat  the  same  way  as  that  in 


THE   NATURE   OF   MIND.  481 

which  we  speak  of  the  product  of  the  field  or  of  the  loom. 
But  only  the  coarsest  and  most  undiscriminating  material- 
ist could  regard  himself  as  saying  what  is  really  valid 
when  he  represents  states  of  knowledge,  feeling,  or  volition, 
as  in  this  sense  of  the  word,  the  "  product "  of  the  brain. 
When,  too,  we  are  told  that  the  brain  " throws  off"  the 
mental  phenomena,  as  a  kind  of  surplusage  —  so  to  speak  — 
of  its  more  legitimate  form  of  activity  by  way  of  molecular 
motions,  we  listen  to  words  to  which  we  are  absolutely 
without  power  to  assign  any  intelligible  meaning. 

There  is  another  and  more  plausible  use  of  the  word 
"  product "  to  describe  the  connection  between  the  cerebral 
centres  and  the  phenomena  of  consciousness.  Suppose  a 
system  of  material  molecules  to  be  acting  under  relations 
to  each  other  which  are  determined  by  the  constitution, 
arrangement,  and  environment  of  the  molecules.  We 
may  then  speak  of  the  new  relations  which  these  same 
molecules  assume  as  the  product  of  their  previous  consti- 
tution and  arrangement,  together  with  whatever  influences 
act  upon  them  from  without  (their  environment).  Thus 
the  functional  activity  of  the  cerebral  centres,  at  each 
moment,  may  be  regarded  as  the  product  of  the  nervous 
substance  of  the  centres  themselves. 

But  this  use  of  the  word  would  only  explain  each 
momentary  condition  of  the  brain  as  arising  out  of  its 
physical  constitution  and  previous  physical  condition.  The 
explanation  is  perfectly  legitimate ;  it  is  the  business  of 
the  physiology  of  the  cerebral  centres  to  carry  such  an 
explanation  as  far  as  possible.  Doubtless  all  the  nerve- 
commotions,  all  the  molecular  changes,  in  the  cerebral 
centres  are,  at  each  moment,  capable  of  being  regarded  as 
"  products,"  under  a  mechanical  theory,  of  antecedent 
changes.  If,  however,  such  a  mechanical  theory  of  the 
behavior  of  the  brain,  regarded  as  a  system  of  material 
beings,  could  be  perfectly  adjusted  to  the  principle  of  the 


482  PHYSIOLOGICAL   PSYCHOLOGY. 

conservation  and  correlation  of  energy,  we  do  not  see  how 
it  would  enable  us  to  regard  the  behavior  of  the  mind  — 
the  phenomena  of  mental  states  —  as  "products"  of  the 
same  antecedent  changes.  Out  of  nerve-commotions,  as 
their  product,  other  nerve-commotions  come.  But  how 
are  the  phenomena  of  knowing,  feeling,  and  choosing 
rendered  any  less  incomparable  with  the  molecular  changes 
of  nervous  matter  by  speaking  of  them,  too,  as  products  of 
the  substance  of  the  brain  ? 

Nervous  Changes  as  Antecedents  of  Mental  Phenomena. — 
But  surely,  it  will  perhaps  be  said,  the  happenings  of 
mind,  the  so-called  states  of  consciousness,  are  dependent 
upon  the  changing  conditions  of  the  brain.  Precisely  so  : 
but  this  does  not  alter  the  necessity  of  assuming  the 
reality  of  mind,  as  the  being  whose  states  change,  though 
in  dependence  on  other  beings  of  a  material  kind.  On  the 
contrary,  if  this  question  were  to  be  referred  to  meta- 
physics we  should  say  that,  to  be  the  subject  of  states 
which  change  in  dependence  on  the  changing  states  of 
other  beings,  is  in  part  the  essence  of  all  reality. 

The  investigations  of  physiological  psychology  furnish 
abundant  proof,  on  the  other  hand,  that  mental  phenomena 
are  the  regular  antecedents  of  changes  in  the  cerebral  cen- 
tres, and  through  these  changes,  of  changes  in  the  other 
bodily  organs.  Indeed,  the  more  comprehensive,  minute, 
and  profound  its  investigations  are,  the  more  convincing 
does  the  evidence  to  this  effect  become.  On  the  whole, 
there  is  as  good  reason  to  regard  the  mind  as  a  reality 
which  influences,  or  acts  upon  the  body,  as  to  regard  the 
body  as  influencing,  or  acting  upon,  the  mind. 

To  emphasize  the  fact  that  nervous  changes  are  the 
regular  antecedents,  or  causes,  of  mental  phenomena,  and 
to  deny  that  mental  phenomena  are  also  changes  of  states 
in  a  real  being,  which  we  call  the  Mind,  is  therefore  to 
treat  the  scientific  data  in  a  one-sided  way.  It  is,  indeed, 


THE  NATURE   OF  MIND.  483 

to  treat  the  psychical  subject  of  states  with  more  disrespect 
than  physics  shows  to  the  mass  or  the  atom.  For  every 
material  mass  or  atom  is  dependent  upon  the  behavior  of 
some  other  similar  mass  or  atom,  for  the  character  of  its  own 
changes,  j  But  physics  does  not,  on  this  account,  deny  its 
reality.  In  its  turn,  by  its  own  behavior,  each  mass  or 
atom  also  furnishes  regular  antecedents,  as  causes,  for 
other  changes  in  the  very  beings  on  which  its  own 
behavior  depends.  These  other  beings,  too,  are  depend- 
ent upon  it  for  the  way  in  which  they  behave.  What 
valid  reason  can  be  given,  why  the  reality  of  mind  should 
be  sunk  wholly  out  of  sight,  in  the  supposed  behalf  of  the 
material  molecules  of  the  cerebrum  ?  Surely  the  souls  we 
know  we  are  should  receive  as  much  consideration  as  the 
elements  of  that  pulpy  mass  we  call  our  brains. 

Superiority  of  the  Mind's  Claim  to  Reality. — For,  in  truth, 
the  claim  of  the  mind  to  a  real  and  independent  existence 
is,  in  some  respects,  unique.  It  is  far  stronger  than  the 
claim  which  can  be  made  for  any  of  the  existences  with 
which  physical  science  deals.  The  materialistic  theory, 
of  course,  assumes  the  very  opposite  of  this.  It  assumes 
that  every  mental  phenomenon  is  to  be  accounted  for 
solely  as  a  manifestation  of  changes  going  on  in  bodily 
reality,  —  in  the  psycho-physical  centres  of  the  brain. 
Nothing  —  says  the  theory  —  can  happen  by  way  of  con- 
scious sensation,  perception,  aesthetic,  or  religious  feeling 
and  belief,  abstract  conception,  or  so-called  free  choice, 
which  does  not  find  its  only  real  explanation  in  the  equiva- 
lent changing  states  of  the  nervous  system. 

Our  first  impression  on  considering  the  foregoing  theory 
is  one  of  surprise  at  its  audacity.  We  have  had  frequent 
occasion  to *  remark  the  extraordinary  difficulties  which 
accompany  the  effort  to  establish  on  scientific  foundations 
almost  every  subordinate  principle  of  physiological  psy- 
chology. Even  in  those  branches  of  its  inquiries  in  which 


484  PHYSIOLOGICAL  PSYCHOLOGY. 

the  methods  of  physical  science  can  be  most  successfully 
employed  (e.g.  Weber's  law,  the  phenomena  of  reaction- 
time,  etc.)  assured  results  are  slow  of  attainment.  Even 
in  such  branches  great  caution  is  requisite  to  guard 
against  too  hasty  generalizations.  But  this  theory  pro- 
poses to  clear  all  barriers  with  a  single  leap,  and  to  estab- 
lish on  the  other  side  of  them  a  complete  speculative 
science  of  the  mind  on  a  basis  of  principles  that  are  recog- 
nized as  applicable  (and  even  then,  not  always  without 
hesitation  and  doubt)  only  to  physical  phenomena. 

But  the  theory  of  materialism  is  not  simply  inadequately 
founded.  It  is  opposed,  not  only  to  the  popular  impres- 
sion (which  assumes  the  reality  of  the  mind,  and  knows 
nothing,  except  by  hearsay,  about  the  existence  of  the 
brain),  but  also  to  certain  conclusions  of  psycho-physical 
science. 

The  incomparability  of  the  two  classes  of  phenomena 
(molecular  agitations  of  the  brain  and  states  of  conscious- 
ness) we  have  seen  to  be  generally  admitted.  The  causal 
relation,  or  dependence  under  law,  of  the  two,  has  been 
shown  to  be  a  legitimate  conclusion  of  science.  But  the 
independent  (in  some  sort)  development  of  the  mind  —  its 
life  and  growth  as  a  non-material  entity,  under  forms  and 
laws  of  unfolding  that  are  unique,  constitutional,  wholly 
peculiar  to  itself  —  is  also  a  legitimate  conclusion  of  the 
same  science.  In  proof  of  this  statement  we  may  fitly 
appeal  to  certain  facts  treated  in  the  preceding  chapters. 

Non-correlated  Factors  of  Mental  Life.  —  All  mental  life 
rests  upon  a  basis  of  sensory-motor  activities.  The  term 
"  sensory-motor,"  however,  may  be  applied  either  to  physi- 
cal or  to  psychical  changes.  As  applied  to  physical  activ- 
ities, the  science  of  physiology  considers  the  data  and  laws ; 
as  applied  to  psychical  phenomena,  the  term  designates  the 
sensation-elements,  the  feelings  of  effort  and  strain,  etc., 
which  enter  into  all  our  life  of  the  body.  Between  these  two 


7 

THE   NATURE   OF   MIND.  485 

classes  of  activities  "correlations,"  in  the  stricter  sense  of 
the  word,  exist.  The  kind,  degrees,  time-rate,  and  "local 
coloring,"  of  the  psychical  factors  depend  upon  the  kinds, 
quantities,  time-rate,  and  locality  of  the  physical  ante- 
cedents. 

But  the  life  of  the  mind  cannot  be  described  solely  in 
terms  of  the  production,  combination,  reproduction,  and 
association  of  sensory-motor  factors.  The  attempt  to  do 
this  induces  the  customary  alliance  between  materialism  and 
sensationalism ;  these  two  are  inclined  to  go  hand  in  hand, 
as  theories  of  mental  life.  The  latter  endeavors  to  expel 
from  existence  those  forms  of  mental  activity  for  which 
the  former  finds  it  most  difficult,  most  impossible,  to 
account. 

But  a  thorough  analysis  of  mental  life  discloses  other 
forms  of  activity  than  those  properly  called  sensory -motor ; 
and  these  forms  not  only  do  not  find  their  full  explana- 
tion in  the  changing  states  of  the  brain,  but  are  not  even 
conceivable  as  correlated  with  such  states.  For  example, 
an  increasing  amount  of  the  sensation  of  pressure  is  not 
identical  with  an  additional  gramme  of  metal  laid  upon 
some  area  of  the  skin ;  but  the  changes  of  quantity  in  the 
sensation  of  pressure  are  correlated,  under  psycho-physical 
law,  with  the  increase  in  the  number  of  grammes.  Into 
my  perception  of  the  piece  of  metal,  as  a  "  Thing  "  causing 
my  sensation,  however,  there  enter  forms  of  purely  psy- 
chical activity  that  cannot  even  be  conceived  of  as  thus 
correlated. 

For  certain  fundamental  assumptions,  or  beliefs,  enter 
into  all  perception  by  the  senses.  No  perception  is  a  mere 
combination  of  sensation-complexes,  representable  in  terms 
of  correlated  changes  of  stimuli  and  of  nerve-commotions. 
Perception  is  a  knowledge  of  "  Things."  No  "  Thing  "  is 
known  as  a  mere  grouping  of  sensation-complexes.  And 
whatever  account  one  may  choose  to  give  of  their  nature 


486  PHYSIOLOGICAL  PSYCHOLOGY. 

and  origin,  there  can  be  no  doubt  that  various  assumptions 
and  beliefs  are  implicated  in  all  knowledge  of  things.  The 
knowledge  of  perception,  then,  involves  an  activity  of 
the  mind  which  is  sui  generis,  —  an  activity  into  the  per- 
formance of  which  the  mind  develops ;  and  which,  although 
it  always  rests  upon  a  basis  of  correlated  physical  changes, 
is  not,  as  such,  representable  as  the  equivalent,  or  corre- 
late of  physical  changes. 

Things  are  known  as  "  real " ;  they  are  believed  to  be 
the  "  subjects "  of  attributes,  to  have,  and  not  to  be,  the 
attributes.  They  are  conceived  of  as  acting  on,  and  as 
being  acted  upon  by,  each  other ;  they  extend  in  an  empty 
space,  which  is  assumed  to  be  self-existent  and  indepen- 
dent of  the  things.  All  this,  and  much  more  of  the  same 
sort,  is  implicated  in  those  mental  acts  which  are  often 
falsely  conceived  of  as  the  mere  passive  reception  of  im- 
pressions ;  or  as  the  combination,  under  terms  dictated  by 
physical  mechanism,  of  sensations  and  feelings  of  bodily 
strain.  But,  in  truth,  all  this  and  whatever  more  is  of 
the  same  sort,  —  we  repeat,  —  implies  being  and  action 
that  are  absolutely  incapable  of  representation  in  terms  of 
such  mechanism.  Nor  can  the  varying  degrees  and  time- 
rates  of  the  movements  of  this  mechanism  be  conceived  of 
as  correlates  of  these  modes  of  the  mind's  behavior. 

What  is  true  of  perception  is  true  of  all  the  developed 
mental  life.  Indeed,  the  form  of  mental  life  we  call  per- 
ception, implies  the  exercise  of  the  so-called  higher  facul- 
ties of  mind.  Physical  changes  in  the  ideo-motor  centres 
of  the  brain  are,  no  doubt,  strictly  correlated  with  certain 
factors  in  that  complex  form  of  the  mind's  acting  to  which 
the  name  of  "  memory  "  is  given.  Here,  too,  a  faded  and 
weakened  sensation,  revived  as  a  memory-image,  may  be 
regarded  the  psychical  equivalent  of  a  weakened  similar 
molecular  agitation  in  the  same  ideo-motor  centre  as  that 
where  the  physical  basis  of  the  original  sensation  was  laid. 


THE  NATURE   OF   MIND.  487 

But  of  what  physical  changes  shall  that  conscious  recogni- 
tion, which  is  the  spiritual  essence  of  all  acts  of  developed 
memory,  be  regarded  as  the  correlate  ? 

Serious  consideration  of  such  a  question  as  the  foregoing 
throws  us  into  the  same  state  of  mind  as  that  in  which  we 
find  ourselves  when  we  ask :  How  many  foot-pounds  is  the 
equivalent  of  a  true  mother's  love  ?  or,  How  many  cubic 
yards  .represent  the  greatness  of  the  thoughts  in  Newton's 
"  Principia  "  ?  My  memory-image  of  the  sensations,  given 
me  by  a  certain  colored  object,  is  —  to  be  sure  —  no  more 
identical  with  the  cerebral  brain-commotions  on  which  it 
depends,  than  were  the  original  sensations  identical  with 
those  original  brain-commotions  on  which  they  depended. 
But  the  image  may  be  said  to  be,  as  respects  quantity, 
quality,  local  coloring,  etc.,  correlated  with  the  revived 
physical  changes  on  which  it  depends.  On  the  contrary, 
the  spiritual  fact  that  I  consciously  recognize  this  present 
experience  called  memory  as  representative  of  my  past 
experience,  and  that  I  attribute  both  present  and  past 
state  to  the  same  self,  —  all  this  implicates  modes  of  men- 
tal life  which  cannot  even  be  conceived  of  as  having  any 
physical  correlates. 

Reality  of  the  Brain  and  its  Processes.  —  It  cannot  escape 
the  acute  thinker  that  the  materialistic  hypothesis  secretly 
assumes  the  reality  and  causal  activity  of  the  cerebral  sub- 
stance and  of  the  physical  changes  which  occur  in  it.  But 
scepticism  can  readily  call  this  assumption  in  question. 
And,  indeed,  the  history  of  philosophy  shows  that  unpreju- 
diced reflection  leads  much  more  directly  and  surely  to 
doubt  about  the  reality  of  matter  than  about  the  reality 
of  mind.  Even  the  science  of  physiological  psychology  — 
at  least  in  some  of  its  aspects  —  tends  to  emphasize  that 
doubt  with  which  the  record  of  speculation  is  so  familiar. 
For  this  science  shows  us  how  very  far  is  the  most  imme- 


488  PHYSIOLOGICAL  PSYCHOLOGY. 

diate  perception  of  the  material  substance  called  brain, 
from  being  a  faithful  copy  of  any  real  existence. 

How  —  to  put  our  doubt  into  the  form  of  a  concrete 
inquiry  —  does  the  holder  of  the  materialistic  hypothesis 
know  that  the  patient,  whose  mental  phenomena  are  ab- 
normal, has  a  brain  to  whose  diseased  condition  he  may 
refer  this  departure  from  the  correct  mental  standard? 
Only  by  inference  from  a  very  few  cases  of  post-mortem,  it 
may  be,  to  a  general  conclusion  respecting  all  human 
bodies.  But  inference  and  conclusion  are  mental  activi- 
ties,—  modes  of  the  behavior  of  conscious  mind.  Infer- 
ence brings  us  to  valid  conclusion,  and  conclusion  to  real 
existence  is  trustworthy,  only  as  reason  puts  confidence  in 
her  own  laws.  These  laws  are  the  constitutional  ways  of 
that  spiritual  procedure  on  which  —  in  the  last  analysis  — 
all  confidence  rests. 

Suppose,  however,  that  those  observations  and  inferences 
in  which  the  science  of  physiological  psychology  delights 
were  indefinitely  extended.  Suppose  that  all  the  sensory- 
motor  functions  were  definitely  localized  in  their  proper 
cerebral  areas ;  that  the  laws  of  the  association  of  these 
areas  were  thoroughly  comprehended ;  that  the  "  nerve 
physiology  "  of  the  brain  had  developed  in  scientific  exact- 
ness so  far  that  the  movements  of  each  molecule  of  its  sub- 
stance could  be  predicted  as  certainly  as  can  now  the 
movements  of  the  planets.  In  brief,  let  it  be  taken  for 
granted  that  the  deficiencies  of  knowledge  which  we  have 
encountered  everywhere  in  our  study  of  this  subject  have 
all  been,  as  fully  as  is  conceivable,  supplied. 

A  completed  science  of  physiological  psychology,  as 
such,  would  not  in  the  least  degree  more  firmly  establish 
the  real  existence  of  any  single  brain  and  its  processes.  A 
completed  science  would  still  be  —  what  the  very  word 
"  science  "  indicates  —  a  system  of  spiritual  activities,  to 
be  assigned  to  the  subject,  Mind. 


THE   NATURE   OF   MIND.  489 

Of  course  it  must  be  understood  that  all  science  is  based 
upon  observation  —  minute,  painstaking,  verifiable,  com- 
prehensive. But  observation  itself  is  a  spiritual  activity, 
involving  immensely  complicated  psychical  factors,  imply- 
ing numerous  assumptions,  beliefs,  and  other  modes  of  the 
behavior  of  the  mind,  which  are  not  capable  of  being 
represented  by,  or  strictly  correlated  with,  those  cerebral 
changes  with  which  physiology  deals. 

We  have,  then,  far  more  direct  and  verifiable  knowledge 
of  the  reality  which  we  ourselves  are,  as  conscious  minds, 
than  of  that  hypothetical  reality  which  materialism  gives 
to  gyrating,  swinging  molecules  in  the  centres  of  the  cere- 
brum. If  one  were  determined  to  reduce  all  being  and 
action,  in  reality,  to  either  of  those  two  sets  of  terms  with 
which  physiological  psychology  assumes  to  deal,  one  must 
certainly  choose  the  psychical  rather  than  the  physical, 
the  terms  represented  by  the  noun  rather  than  the  adjec- 
tive, in  the  compound  title. 

Reality  of  Mental  Development.  —  That  the  words,  "  devel- 
opment of  the  mind,"  stand  for  a  real  process,  there  can  be 
no  reasonable  doubt.  What  is  true  of  every  developed 
mental  activity  is,  even  more  palpably  and  emphatically, 
true  of  the  entire  course  of  mental  development.  It  can- 
not be  adequately  described  as  a  mere  series  of  more  and 
more  complex  combinations  of  psychical  factors  of  the 
sensory-motor  type.  The  difference  between  those  incon- 
ceivably simple  activities  in  which  mental  life  begins  and 
the  more  mature  and  highly  developed  mental  activities 
is  not  a  difference  of  degree  alone.  Newton  or  Kant,  as  a 
mind,  is  far  more  unlike  the  infant  than  the  latter  is  unlike 
one  of  the  lower  animals.  There  is  much  more  which  is 
companionable  and  mutually  intelligible  between  a  man 
and  his  dog  than  between  a  man  and  his  newly  born 
child. 

The  changes  which  lie  between  the  first  and  lowest,  and 


490  PHYSIOLOGICAL  PSYCHOLOGY. 

the  more  mature  and  highest  things  of  human  mental  life 
occur  according  to  a  plan.  The  life  of  every  mind  is  capa- 
ble of  being  made  the  subject  of  a  history.  This  history 
has  its  epochs  and  crises;  it  has,  as  well,  its  periods  of 
more  steady  and  unobtrusive  growth.  But,  on  the  whole, 
it  implies  the  development  of  that  real  being,  whose  mani- 
festation is  indeed  related  to  the  growth  and  activity  of 
the  cerebral  mechanism,  but  whose  character  is  unique 
among  all  developments  —  the  so-called  "  human  Mind." 

Nor  does  the  uniqueness  of  the  mind's  development 
consist  alone  in  that  admitted  incomparability  of  the  phe- 
nomena of  conscious  sensation  to  all  physical  phenomena, 
to  which  reference  has  already  frequently  been  made.  In 
all  developments  of  a  physical  sort,  —  even  including  those 
with  which  biology  deals,  —  the  factors  which  take  part  in 
the  development  are  themselves  really  existing  entities, 
regarded  by  science  as  endowed  with  natures  and  powers 
innumerable  of  their  own.  The  development  of  living 
things,  including  the  development  of  the  nervous  system 
itself,  is,  according  to  science,  nothing  but  the  more  and 
more  complicated  and  planful  concourse  of  "  the  atoms." 
These  atoms  are  really  existing  beings.  But  simple 
sensations,  and  sensation-complexes,  and  elementary  feel- 
ings or  "feelings  of  feelings,"  and  memory-images,  etc., 
although  they  are  regarded  by  mental  science  as  factors  in 
mental  life,  are  not  really  existing  beings  at  all.  And 
every  attempt  at  a  system  of  psychology  which  treats  them 
after  the  analogy  of  the  elements  of  a  physical  develop- 
ment overlooks  the  entire  nature  of  the  problem  to  be 
solved.  <* 

The  life  of  the  mind,  as  it  manifests  itself  for  scientific 
study,  is  a  succession  of  "  fields  of  consciousness."  None 
of  these  so-called  "  fields  of  consciousness "  can  be  con- 
sidered as  accounting  for  itself.  All  of  them  are  forth- 
puttings  of  that  living  being  which  is  the  subject  of  them 


THE   NATURE   OF  MIND.  491 

all.  They  fade  into  each  other ;  they  enlarge  and  diminish 
in  circuit ;  they  succeed  each  other  with  a  varying  time-rate. 
Psychological  science  analyzes  them  into  their  hypothet- 
ical factors ;  it  tries  to  determine  the  uniform  conditions 
of  their  formation,  and  the'  laws  according  to  which 
they  follow  each  other.  It  finds  them  all  hung  together, 
as  it  were,  upon  a  single  thread,  —  upon  the  metaphysical, 
the  shadowy  but  necessary,  assumption  of  the  existence 
of  one  entity,  the  soul,  whose  states  they  all  are.  No  self- 
consciousness  is  so  penetrating  and  lively  as  to  envisage 
this  entity  in  its  pure  being,  or  naked  simplicity,  as  a 
subject  of  all  the  states.  But  every  act  of  self-conscious- 
ness is  a  reference  of  some  state  to  this  assumed  subject  of 
them  all.  And  science  can  do  nothing  with  the  phe- 
nomena of  mind  without  virtually  assuming  that  being 
whose  life  and  development  binds  together  its  own  suc- 
cession of  "  fields  of  consciousness,"  so-called. 

The  attempt  to  regard  the  planful  unfolding  of  fields  of 
consciousness,  which  constitutes  the  life  of  the  mind,  as 
merely  the  resultant  of  a  physical  evolution  of  the  nervous 
system,  involves  a  constant  abuse  of  terms.  It  makes 
inevitable  that  mistaking  of  figures  of  speech  for  scientific 
truths,  against  which  we  have  already  protested  once  and 
again.  Terms  which  apply  well  enough  to  a  biological 
evolution,  when  applied  to  the  development  of  the  mind, 
have  no  intelligible  meaning  at  all.  The  word  "  develop- 
ment "  itself,  when  applied  to  the  mind,  means  something 
entirely  different  from  the  same  word  when  applied  to  an 
organic  structure  like  the  cerebro-spinal  system.  At  every 
step  we  have  to  check  our  descriptions  of  the  growth  of  the 
soul's  life  by  asking :  "  Precisely  what,  then,  is  it  that  we 
mean  ?  " 

But  even  if  we  disregarded  the  bearing  of  such  a  process 
of  misleading  substitution  in  the  meaning  of  terms,  we 
should  still  have  valid  reasons  for  affirming  the  reality  of 


492  PHYSIOLOGICAL   PSYCHOLOGY. 

the  mind's  unfolding  life.  For  the  process  of  this  unfold- 
ing, so  far  as  we  really  know  in  what  it  consists,  and  upon 
what  physical  conditions  it  is  dependent,  does  not  keep 
equal  step  with  the  evolution  of  the  nervous  system.  It 
is  indeed  customary  for  psycho-physical  science  to  assume 
that  mind  and  brain  develop,  as  it  were,  hand  in  hand ; 
and  that  the  dependence  of  the  former  upon  the  latter  is 
so  strict  as  to  make  all  mental  growth  really  an  expression 
of  a  physical  evolution.  Still,  on  this  point,  we  believe 
that  the  popular  impression  emphasizes  certain  facts  which 
the  ordinary  scientific  hypothesis  is  apt  to  leave  out  of 
account. 

For  example,  at  the  time  of  birth  the  mind  appears 
almost  or  quite  wholly  undeveloped ;  although  the  brain 
of  the  full-grown  embryo  is,  as  respects  both  structure  and 
functions,  a  highly  developed  affair.  The  human  infant 
has  by  far  the  most  complexly  organized  and  fully  equipped 
nervous  system  of  any  of  the  young  animals.  But  it  has, 
properly  speaking,  little  or  no  mind.  It  is  a  truly  sig- 
nificant figure  of  speech  which  regards  the  mind  of  the 
infant  as  yet  unawakened ;  as,  indeed,  waiting  to  be  aroused 
and  set  to  the  work  of  combining  and  interpreting  those 
sensations  which  are  called  forth  by  the  excitation  of  its 
nervous  system. 

Nor  do  we  know  of  any  valid  reason  for  disputing 
the  apparent  truth  that,  immediately  after  birth,  the  in- 
fant's mind  develops  with  a  more  rapid  step  than  is  taken 
by  the  organic  evolution  of  the  brain.  That  the  brain 
grows  with  a  marked  rapidity,  not  only  in  gross  weight 
but  also  in  complexity  of  structure,  during  the  first  year 
of  life,  is  a  significant  fact.  That  the  sensory-motor  factors 
of  psychical  growth  are  dependent  upon,  and  correlated 
with,  this  physical  growth,  we  do  not  for  a  moment  ques- 
tion. We  also  regard  as  entirely  plausible  the  view,  that 


THE  NATUKE   OF  MIND.  493 

innumerable  "  dynamical  associations  "  are  rapidly  forming 
themselves  in  the  child's  cerebral  hemispheres. 

But,  on  the  other  hand,  a  comparison  of  the  character 
of  the  mental  life  at  the  close  of  the  first  year — its  un- 
folding of  the  powers  of  perception,  voluntary  attention 
and  abstraction,  under  those  constitutional  norms  which 
philosophy  calls  the  "  intuitions  "  or  "  categories  "  —  with 
the  absence  of  all  really  mental  life  at  birth,  suggests  another 
view  of  the  case.  The  evolution  of  the  brain  is  not  a 
complete  measure,  much  less  is  it  a  complete  explanation, 
of  the  growth  of  the  life  of  the  mind. 

Similar  arguments  against  the  view  which  regards  the 
mental  development  as  only  an  expression  or  resultant  of 
the  organic  evolution  of  the  brain,  might  be  derived  from 
other  periods  and  phases  of  life.  It  should  never  be  for- 
gotten that  when  we  are  describing  the  character  and 
causes  of  mental  development  in  terms  of  a  spiritual  real- 
ity and  a  spiritual  life,  we  are  speaking  of  that  which  all 
men  know.  Mental  curiosity,  control  of  attention,  careful 
and  comprehensive  judgment,  sound  moral  purpose  — 
these  words  represent  terms  of  universal  and  undoubted 
experience.  That  the  development  of  the  mind  depends 
upon,  and  consists  in,  these  things,  is  beyond  all  question. 
That  these  things  are  only  the  expressions  or  resultants  of 
organic  brain-changes,  is  a  hypothesis  which  most  men 
find  it  difficult  to  comprehend ;  and  which,  in  our  judg- 
ment, no  man  has  any  right  to  propose  as  a  scientific 
necessity  or  even  as  a  valid  scientific  faith. 

We  regard  the  following  statement,  then,  as  justified : 
The  development  of  mind  can  only  be  explained  as  the  pro- 
gressive manifestation  in  consciousness  of  the  life  of  a  real 
being,  which,  although  taking  its  start  and  direction  from 
the  action  of  the  physical  elements  of  the  body,  proceeds  to 
unfold  powers  that  are  sui  generis,  according  to  laws  of  its 
own. 


494  PHYSIOLOGICAL  PSYCHOLOGY. 

The  mind  is  a  "real"  being  in  the  highest  sense  in 
which  any  finite  being  can  be  said  to  be  real.  Indeed,  its 
claim  to  be  considered  real  is  more  indisputable  than  the 
same  claim  as  put  forth  for  any  material  thing ;  it  is 
unique.  The  reality  of  mind  underlies  and  makes  possi- 
ble all  our  knowledge  of  other  real  beings ;  and  all  our 
assumptions  as  to  the  existence  of  such  beings.  It  is  only 
on  condition  of  granting  its  reality,  in  the  highest  sense 
of  the  word,  that  we  can  affirm  the  reality  of  other  beings. 

Unity  of  the  Mind.  —  Among  the  terms  by  which  we  char- 
acterize the  peculiar  nature  of  that  being  we  call  the  mind, 
there  is  none  more  important  than  the  term  "  unity."  The 
popular  impression  regards  every  person,  every  soul  or 
mind,  as  one,  in  a  perfectly  unique  way.  It  is  not  difficult 
to  make  clear  to  the  popular  impression  that  we  may  speak 
of  all  material  existences  as,  at  the  same  time,  one  and 
many,  —  according  to  the  point  of  view  from  which  they 
are  regarded.  In  the  study  of  perception  it  was  evident 
that  the  unity  of  any  object  of  sense  is  imparted  to  it  by  a 
constructive,  synthetic  action  of  the  perceiving  mind. 
Molecular  science  at  once  proceeds  to  analyze  the  object 
of  perception  into  a  countless,  an  inconceivably  great,  num- 
ber of  constituent  elements.  The  elements  are  regarded  as 
even  more  truly  units  than  is  the  object  of  perception 
itself. 

The  physical  unity  which  science  thus  allows  every 
object  to  have  is  gained  only  as  its  constituent  elements 
are  temporarily  held  together  by  various  so-called  "  forces," 
according  to  a  variety  of  forms  called  "  laws."  The  only 
unity,  in  the  stricter  sense  which  physical  science  recog- 
nizes, is  that  said  to  belong  to  the  atom  ;  but  in  what  this 
unity  consists  it  is  difficult  to  make  clear  to  the  mind. 
Indeed,  the  trained  imagination  of  the  physicist  is  scarcely 
adequate  to  depict  the  nature  of  this  hypothetical  unity. 

Mental  Unity  not  Analogous  to  Physical.  —  Whatever  kind 


THE   NATURE   OF   MIND.  495 

of  unity  physical  science  may  finally  succeed  in  indicating 
for  the  individual  atoms,  it  is  obvious  that  such  atomic 
unity  furnishes  no  fitting  analogy  for  the  case  of  the  mind. 
Indeed,  we  ought  here  to  reverse  the  entire  order  of  pro- 
cedure. The  unity  which  the  atoms  are  assumed  to  have, 
is  due  to  the  unifying  act  of  the  mind  which  thus  con- 
ceives of  the  atoms.  Whether  these  conceptions  fitly  rep- 
resent any  eatfra-mental  realities,  we  do  not  now  inquire. 
But  whether  they  do,  or  not,  there  can  be  no  doubt  that 
the  only  atoms  known  are  the  atoms  conceived  of  (as  real, 
or  not)  ;  and  the  only  being  that  conceives  of  atoms,  or  of 
anything  else,  is  the  mind. 

The  foregoing  fact  does  not  necessarily  favor  that  old- 
fashioned  hypothesis  which  regarded  the  unity  of  the 
mind  as  somewhat  analogous  to  the  unity  of  a  homo- 
geneous and  eternally  unchanging  material  substance. 
Indeed,  modern  physical  science  does  not  regard  even  the 
atoms  as  "  unit-beings,"  in  such  a  meaning  of  the  word. 
It  was  the  theological  interest  in  the  attempt  to  place  the 
immortality  of  mind  upon  a  quasi-scientific  basis  which 
gained  favor  for  this  uncouth  view.  The  argument  ran : 
The  immortality  of  the  mind  depends  upon  its  natural 
indestructibility ;  that  which  is  indiscerptible  or  indivisible 
is  naturally  indestructible  ;  and  that  which  is  indiscerptible 
must  be  a  unity  in  the  strictest  sense  of  the  word. 

It  is  impossible  to  see,  however,  why  a  physical  being 
which  has  no  distinction  of  parts,  and  undergoes  no 
changes  of  states,  is  best  fitted  to  represent  the  unity  of 
mind-being  and  mind-life.  Indeed,  the  very  opposite  of  this 
is  obviously  true.  Comparative  study  shows  us  that,  as  a 
rule,  the  more  complex  and  varied  is  the  psychical  life  of 
any  animal,  the  more  complex  and  varied  is  the  grouping 
of  that  collection  of  organs  which  constitutes  its  nervous 
"system"  so-called.  But  the  highest  unity  of  mental  life 
is  that  which  is  built  upon  the  greatest  variety  and  com- 

• 


496  PHYSIOLOGICAL   PSYCHOLOGY. 

plexity  of  psychical  activities.  It  is  man  who,  among  all 
the  animals,  has  by  far  the  best  claim  to  be  considered  a 
"  unit-being,"  as  regarded  from  the  psychological  point  of 
view.  But  it  is  man  who  has  also  the  most  elaborate  and 
complicated  development  of  material  organs,  —  systema- 
tized into  a  cerebro-spinal  axis  and  crowned  by  that  peer- 
less structure,  a  human  brain. 

Nor  is  this  cerebro-spinal  nervous  system,  which  forms 
the  physical  basis  of  the  unity  in  variety  of  man's  mental 
life,  a  homogeneous  and  unchanging  mass.  Far  from  it. 
No  other  portion  of  the  bodily  substance  demands  such  a 
copious  blood-supply ;  undergoes  such  rapid  and  important 
changes  with  respect  to  those  "  dynamical  associations  "  on 
which  the  psychical  habits  of  memory  depend ;  and  is,  in 
general,  so  ceaselessly  active  in  producing  inconceivably 
complex  molecular  variations  in  its  own  condition  and 
constitution.  Corresponding  to  this  physical  system  of 
innumerable  interacting  elements  and  parts  is  an  almost 
boundless  variety  to  the  sensory-motor  psychical  life.  For, 
as  we  have  already  seen,  certain  single  senses  are  capable 
of  hundreds  of  thousands  of  sensations  that  can  be  distin- 
guished by  minute  variations  in  quantity,  quality,  and 
"  local  coloring."  Or,  more  properly  speaking,  in  re- 
sponse to  the  excitation  of  this  wonderful  nervous  mechan- 
ism in  a  countless  variety  of  ways,  the  soul  puts  forth  a 
corresponding  variety  of  those  forms  of  manifestation 
which  are  peculiar  to  its  life. 

But  all  this  is  far  from  being  incompatible  with  that 
unitary  nature  and  existence  which  is  possessed  by  every 
human  soul.  In  spite  of  what  we  might  argue  as  to  the 
possible  or  impossible  in  such  a  case,  the  fact  remains  that, 
in  the  order  of  nature,  this  very  being  which  has  such  an 
inconceivable  complexity  of  physical  and  psychical  activi- 
ties is  a  "  unit-being,"  in  the  very  highest  sense  of  the 
word. 


THE   NATUKE   OF   MIND.  497 

The  unity  which  the  mind  possesses  is  undoubtedly 
dependent  upon  memory  and  self -consciousness.  It  is  that 
spiritual  unity  which  implies  the  power  of  knowing  one's 
self,  —  of  having  states  not  only,  but  also  and  chiefly,  of 
referring  these  states  to  the  unity  of  Self,  and  of  distin- 
guishing, in  consciousness,  that  Self  as  a  unique  consistent 
development,  from  all  other  selves  and  from  all  things. 
So  peculiarly  is  this  a  function  of  the  developed  mind,  or 
soul,  that  the  words,  a  mind,  or  a  soul,  are  absolutely 
devoid  of  meaning  unless  they  are  understood  as  implica- 
ting this. 

It  is  quite  possible,  indeed,  to  raise  that  sceptical  ques- 
tion, of  which  Kant  makes  so  much  in  his  immortal  "Cri- 
tique of  Pure  Reason."  After  all,  —  we  may  ask,  —  is  the 
mind  in  reality  one ;  or  does  it  only,  when  normally 
active,  seem  to  itself  to  be  one?  The  valid  reply  to  this 
question  is  as  follows :  The  unity  of  a  self-conscious 
rational  life  is  the  highest  and  realest  of  all  conceivable 
unities.  In  other  words,  to  be  a  developing  mind,  with 
memory,  reason,  and  self-consciousness,  —  this  is  to  be 
really  one.  It  is  this  unity,  which  the  mind  undoubtedly 
has  in  self-consciousness,  that  is  alone  worth  contending 
for.  And  if  the  mind  were  really  —  that  is,  regarded  as 
out  of  its  own  consciousness  of  self  —  one,  and  yet  two  or 
more  in  consciousness,  it  would  be  no  better,  but  rather 
the  worse  off.  If  it  were  really  one,  but  could  not  appear 
to  itself  as  one,  could  not  be  aware  of  its  own  change  of 
states,  and  attribute  them  to  the  one  Self,  which  is  the 
subject  of  them  all,  its  unity  would  be  of  no  value. 

Once  more:  a  thorough  metaphysical  analysis  would 
probably  show  us  that  the  unity  which  we  attribute  to 
things  is  never  more  than  a  pale  shadow,  or  faded  type,  of 
the  unity  which  we  know  ourselves  to  have.  Physics, 
indeed,  regards  the  atom  as  the  only  unity,  in  the  strictest 
sense  of  the  word.  But  this  so-called  "strictest  sense  of 


498  PHYSIOLOGICAL  PSYCHOLOGY. 

the  word "  is  itself  (probably)  copied  from  that  type  of  all 
reality,  which  is  the  unit-being,  Mind.  Only  as  the  mind 
of  the  physicist  projects,  into  the  hypothetical  being  of  the 
atom,  the  attributes  of  its  own  life,  can  he  call  the  atom  a 
unit,  in  "  the  strictest  sense  of  the  word."  This  is  done 
with  that  recognition  of  a  kinship  of  all  beings  with  mind, 
which,  after  all,  enters  into  every  scientific  conclusion  or 
hypothesis. 

Spirituality  of  Mind,  —  The  question  whether  we  are  to 
speak  of  the  mind  as  "  spiritual  "  or  not,  scarcely  merits  the 
grave  and  lengthy  discussion  to  which  it  has  often  been 
carried.  "  Materiality,"  as  predicated  of  any  real  being,  is 
only  an  abstract  and  complex  term,  summing  up  a  number 
of  so-called  attributes.  The  word  "  attributes "  is  an 
abstract  term  signifying  the  uniform  ways  of  the  behavior, 
as  known  to  us,  of  individual  things. 

Now,  if  we  understand  the  term  "  materiality  "  correctly, 
we  cannot  think  seriously  of  applying  it  to  the  mind.  For 
the  attributes  which  it  covers  are  such  as  extension,  im- 
penetrability, mass,  etc. ;  and  only  in  a  figurative  way  can 
such  terms  as  those  be  appl  1  to  the  subject  of  psychical 
states.  If,  on  the  contrary,  we  use  the  term  "  spirituality  " 
as  an  abstract  term  to  cover  those  attributes  which  things, 
as  perceived  by  mind,  dc  ^ot  possess,  but  which  minds 
know  themselves  as  posse^ng  and  exercising ;  why  then, 
of  course,  we  must  affirm  the  spirituality  of  mind. 

As  soon,  however,  as  we  attempt  to  conceive  of  the  sub- 
stance of  mind  after  the  analogy  of  some  ethereal  exten- 
sion, some  more  than  ^dinarily  subtile  expression  of  a 
substratum  common  to  .±  beings,  we  lose  our  right  bo^h 
to  affirm  the  spirituality  and  to  deny  the  materiality  of 
mind.  Nor  can  we  hope  scientifically  to  indicate  for  the 
mind  such  "  spirituality  "  as  would  bt  *  its  being 

freed  from  all  relations  to  things,  or  from  dependence  for 
the  modes  of  its  being  upon  the  material  substratum  of  the 


THE  NATURE   OF   MIND.  499 

brain.  How  spirit,  in  the  meaning  of  unembodied  mind, 
would  perceive,  and  feel,  and  think,  and  will,  is  a  question 
toward  the  answer  of  which  psycho-physical  science  enables 
us  to  make  no  beginning  at  all. 

The  subjects  which  we  have  been  considering  have  a  cer- 
tain legitimate  bearing  upon  speculative  inquiries  into  the 
first  and  the  last  things  of  Mind,  —  its  origin  and  destiny, 
its  mortality  or  corruptibility.  Physiological  psychology 
cannot  explain  the  being  of  mind  as  arising  out  of  the 
development  of  the  physical  germ  from  which  the  bodily 
members  unfold  themselves.  It  shows  no  decisive  reason 
against  the  belief  that  such  a  non-material  and  real 
"  unit-being,"  as  the  mind  is,  should  exist  in  other  rela- 
tions than  those  of  its  present  admitted  dependence  upon 
the  structure  and  functions  of  the  body.  But  we  have 
already,  perhaps,  somewhat  transgressed  the  limits  which 
most  authorities  would  set  to  legitimate  conclusions  from 
this  science.  Questions  relating  to  the  origin  and  destiny 
of  that  subject  of  all  the  psychical  states,  whose  reality  and 
unity  we  believe  capable  of  defence  on  scientific  grounds, 
must  be  left  to  Rational  Ps'j  .  itaology,  to  Ethics,  to  Meta- 
physics, and  to  Theology. 


INDEX. 


Allen,  Grant,  on  nature  of  feeling, 

384  f. 
Aphasia,  phenomena  of,  218  f . ;  kinds 

of,  219  f . 

Aqueduct  of  Sylvius,  53. 
Aqueous  Humor,  the,  81. 
Arachnoid,  the  structure  of,  35  f. 
Attention,  effect  of,  on  reaction-time, 

367  f .,  378  f . ;  physical  basis  of,  431  f . ; 

effect  of,  on  perception  and  memory, 

434  f. 
Automatic  Action,  nature  of,  135  f.; 

in  spinal  cord,  140  f.;   and  brain, 

149  f.;    physical  basis  of  volition, 

431  f. 

Bain,  theory  of  feeling,  384  f. 

Bell,  Sir  Charles,  discovery  of,  70. 

Betz,  "  giant-cells  "  of,  67. 

Birge,  E.  A.,  on  number  of  nervous 
elements,  28. 

Blastoderm,  the,  105  f. 

Bliud-spot  (papilla  optica) ,  89  f . 

Body,  early  development  of,  446  f.; 
relative  proportions  in,  450  f. ;  sex- 
ual differences  of,  453  f.;  general 
relations  of,  to  mental  phenomena, 
465  f. 

Brain,  chemistry  of,  12  f.;  membranes 
of,  35  f.;  structure  of,  46  f.,  55  f.; 
hemispheres  and  lobes  of,  55  f . ;  ven- 
tricles of,  60  f.;  ganglia  of,  60  f . ; 
cortex  of,  65  f . ;  inhibitory  influence 
of,  142  f.,  149  f.;  as  central  organ, 
149  f.;  temperature  of,  179  f.;  com- 
parative weight  of,  181  f . ;  weight  of 
human,  182  f . ;  relation  of,  to  mind 
469  f. 

Broca,  convolution  of,  292  f. 

Capsule,  the  internal,  63. 
Cells,  the  olfactory,  75  f.;  the  gusta- 
tory, 76  f.;  the  auditory,  98. 


Central  Canal,  45  f. 

Derebellar  tract,  45  f. 

Cerebellum,  structure  of,  51  f. ;  func- 
tions of,  152  f. 

Cerebrin,  13. 

Cerebro-spinal  system,  axis  of,  35  f. ; 
development  of,  107  f. 

Cerebrum,  shape  of,  55  f. ;  gyri  and 
sulci  of,  59  f. ;  layers  in  its  cortex, 
65  f.;  fibres  of,  67  f.;  nervous  ele- 
ments in,  91,  95  f.;  functions  of,  185 
f.;  localization  in,  187  f.,  196  f.,  204 
f.,  212  f. 

Chemistry,  of  nervous  system,  11  f. ; 
physiological  function,  15  f.;  of  vis- 
ion, 90  f. 

Cholesterin,  13  f. 

Choroid,  the,  90  f . 

Clarke,  columns  of,  42  f. 

Cochlea,  the,  96  f. 

Color,  stimulus  of,  255  f. ;  tones  of, 
256  f. ;  brightness  of,  258;  comple- 
mentary, 260  f.;  dependence  of,  on 
time,  261;  and  place  of  the  retina, 
261 ;  blindness  to,  262  f . ;  contrast 
of,  264 ;  Young-Helmholtz  theory  of, 
265  f.;  symbolism  of,  268  f. 

Consciousness,  the  circuit  of,  377  f.; 
physical  basis  of,  417  f . ;  psycho- 
physical  explanations  of,  418  f.; 
unity  of,  494. 

Cornea,  structure  of,  79  f.;  index  of 
refraction  of,  84. 

Corona  Radiata,  67  f. 

Corpus  albicans,  61  f. 

Corpus  callosum,  55;  function  of,  68. 

Corpus  dentatum,  of  the  medulla,  50; 
of  the  cerebellum,  52. 

Corpus  geniculatum,  60. 

Corpus    quadrigeminum,  position  of, 

62;  functions  of,  153  f. 
Corpus  striatum,  63;    paths    in,  72; 
functions  of,  155  f. 

501 


502 


INDEX. 


Cortex  of  Cerebrum,  structure  of,  65  f. 
Crura  Cerebri,  63 ;  functions  of,  151. 
Crystalline    Lens,    the    structure    of, 

82  f. 

Deiters,    processes    of,    26;     conical 

hair-cells  of,  98. 
Bonders,  time   of   mental   processes, 

359  f.,  373. 

Dove,  the  experiment  of,  338. 
Du  Bois-Reymond,  discoveries  of,  125 ; 

theory  of  nervous  action,  169  f. 
Dura  Mater,  structure  and  processes 

of,  39. 

Ear,  91  f . ;  the  external,  91  f . ;  the 
middle,  92  f.;  tympanum  of,  92; 
the  internal,  95  f.;  vestibule  and 
canals  of ,  95  f. ;  cochlea  of,  96;  nerve 
of,  98  f. ;  development  of,  114  f. ; 
sensitiveness  of,  248,  282. 

Ebbinghaus,  on  memory,  427,  440  f. 

Ecker,  charts  of,  205  f . 

Electricity,  "current  of  rest"  in 
nerves,  125,  169;  as  stimulus  of 
nerves,  125  f. ;  "  negative  variation  " 
in  nerves,  168  f. 

Electrotonus,  Pfliiger's  law  of,  127  f ; 
theory  of,  168  f.,  170  f. 

Embryo,  knowledge  of,  103  f . ;  of  the 
fowl,  104  f.;  development  of,  107  f.> 
1131 

Encephalon,  see  Brain. 

End-organs  of  Motion,  place  in  ner- 
vous system,  32  f. ;  structure  of,  102. 

End-organs  of  Sense,  place  and  signifi- 
cance of,  32  f . ;  end-organs  of  smell, 
74  f. ;  of  taste,  75  f . ;  of  touch,  77  f . ; 
of  sight,  79  f . ;  of  hearing,  91  f. 

Eustachian  Tube,  93  f. 

Exner,  views  of,  on  localization,  204  f. 

Eye,  structure  of,  79  f . ;  tunics  of,  79  f. 
refracting  media  of,  81 ;  appendages 
of,  81  f.;  muscles  of,  81  f. ;  problem 
of,  82  f. ;  adjustment  of,  84  f.;  pig- 
ments of,  90  f. ;  development  of, 
113  f . ;  motion  of,  327  f . ;  meridians 
of,  328;  torsions  of,  329  f.;  stereo- 
scopy  of,  332  f. 

Fasciculus  Gracilis,  48. 
Fechner,  law  of,  276  f. 
Feeling,  of  innervation  or  effort,  404  f . ; 


of  "double  contact,"  321  f. ;  nature 
of,  379  f . ;  classes  of,  388  f . ;  inten- 
sity of,  392;  tone  of,  390  f.;  of  sen- 
sation, 393  f.;  the  emotions,  400  f. ; 
the  higher  aesthetic  and  intellectual, 
395  f . 

Ferrier,  centres  of,  197  f. 

Filum  terminale,  28. 

Fissures,  of  Sylvius,  57;  of  Rolando, 
57  f. 

Flourens  on  respiratory  centre,  147. 

Foramen  magnum,  28. 

Formatio  reticularis,  in  the  medulla, 
50 ;  in  the  tegmentum,  53  f . 

Fovea  centralis,  89. 

Fritsch,  experiments  of,  188. 

Ganglia,  the  "  basal,"  60  f. 
Ganglion-cells,  see  Nerve-cells. 
George,  theory  of  temperament,  457. 
Gerlach,  on  intimate  structure  of  the 

cord,  43. 
Goldscheider,     on     "pressure-spots," 

237  f.;  temperature-spots,  239  f. 
Goll,  column  of,  see  Fasiculus  Gracilis. 
Goltz,  experiments  of,  on  spinal  cord, 

141;  view  of  localization,  223. 
Gyri  (or  convolutions)  of  the  cerebrum, 

59  f . ;  development  of,  112  f . 

Hall,  G.  Stanley,  on  perception  of  mo- 
tion, 314. 

Hearing,  end-organ  of,  91  f.,  114;  sen- 
sations of,  245  f.;  perceptions  of, 
306  f. 

Helmholtz,  accommodation  of  eye,  84 
f.;  on  speed  of  nervous  processes, 
132;  nature  of  noises,  252  f. ;  con- 
sonances of  tone,  253  f. ;  theory  of 
color-sensations,  266  f. 

Herbart,  theory  of  feeling,  385  f. 

Hering,  on  temperature-sensations,240; 
theory  of  color-sensations,  267  f. 

Hermann,  on  theory  of  nervous  action, 
169  f. 

Hitzig,  experiments  of,  188;  centres 
of,  196  f. 

Horopter,  calculation  of,  335  f. 

Horsley  and  Schafer,  experiments  in 
localization,  200  f. 

Inhibition,  from  brain  on  cord,  142  f. ; 
nature  of,  437  f . 


INDEX. 


503 


Iris,  the,  80. 
Island  of  Reil,  59. 

Jackson,  Hughlings,  on  cerebral  local- 
ization, 187  f. 

James,  Professor,  on  the  feeling  of 
effort,  406 ;  laws  of  association,  424. 

Jastrow,  on  comparative  judgments  of 
eye  and  hand,  358  f . 

Krause,  end-bulbs  of,  78. 

Kiihne,  on  chemistry  of  retina,  90  f. 

Kussmaul,  on  aphasia,  222. 

Lecithin,  14. 

Le  Conte,  on  nature  of  the  horopter, 
335.  -C-  ^S- 

Listing,  the  law  of,  329  f. 

Local  Signs,  theory  of,  294,  298  f .,  327. 

Lotze,  theory  of  local  signs,  294  f., 
298  f . ;  errors  of  sense,  349 ;  theory 
of  feeling,  383  f . ;  differences  of  the 
sexes,  456;  kinds  of  temperament, 
458  f. 

Luys,  on  basal  ganglia,  73. 

Magendie,  discovery  of,  70. 

Materialism,  views  of,  479  f. 

Matteucci,  on  electrotonus,  170. 

Mechanism,  nervous  system  as,  7  f. ; 
the  nerve  as,  120  f.;  theory  of  the 
nervous,  158  f. 

Medulla  Oblongata,  structure  of,  47  f . ; 
reflex-motor  functions  of,  146  f . 

Meissner,  calculation  of  the  horopter, 
325. 

Membranes,  of  the  brain,  35  f. ;  the 
basilar,  and  of  Reissner,  97. 

Memory,  physiological  study  of,  419  f . ; 
as  retentive,  419  f. ;  as  reproductive, 
424  f . ;  physical  basis  of,  425  f . ;  psy- 
chological nature  of,  428  f. 

Mesencephalon,  development  of,  111. 

Meynert,  description  of  brain,  69. 

Mills,  on  localization  of  cerebral  func- 
tion, 208  f.,  217. 

Mind,  subject  of  phenomena,  3  f .,  479  f . ; 
relation  to  the  brain,  463  f.,  466  f. ; 
480  f. ;  synthetic  act  of,  in  percep- 
tion, 292  f.,  302  f.,  360  f.;  physical 
explanations  of,  478  f.,  482  f. ;  as  a 
real  being,  478  f. ;  as  a  unit  being, 
494  f . ;  spirituality  of,  498  f. 


Motions,  the  bodily,  classes  of,  407  f.; 
the  impulsive,  409  f . ;  the  voluntary, 
410  f.;  the  expressive,  412  f.  " 

Mtiller,  J.,  on  brain  as  measure  of 
intelligence,  181. 

Munsterberg,  on  memory  and  will,  435, 
440  f. 

Munk,  experiments  of,  198  f. ;  motor 
areas  of,  199  f.;  visual  areas  of, 
213  f . ;  auditory  area  of,  218. 

Nerve-cells,  elements  of  nervous  sys- 
tem, 17  f. ;  kinds  of,  24  f.;  intimate 
structure  of,  25  f . ;  processes  of,  26 ; 
functions  of,  116. 

Nerve-commotion,  causes  of,  116  f.; 
conditions  of,  121  f. ;  nature  of, 
127  f. ;  laws  of,  130  f.;  speed  of,  132 ; 
summation  and  facilitation  of,  165  f. 

Nerve-fibres,  elements  of  nervous  sys- 
tem, 18  f.;  kinds  of,  19  f.;  struc- 
ture of  the  medullated,  21  f.;  fibril- 
lated  axis-cylinder  of,  23  f . ;  size  of, 
24 ;  origin  of,  26  f ^ 

Nerve-muscle  machine,  120  f.;  behavior 
under  electricity,  125  f . 

Nerves,  structure  of,  18  f. ;  kinds  of, 
19  f.;  the  cranial  and  spinal,  36  f.; 
general  function  of,  116  f.,  118  f. ; 
exhaustion  of,  121  f.;  properties  of, 
123  f. ;  thermic  and  chemical  influ- 
ences on,  124  f. 

Nervous  Matter,  kinds  of,  12  f.;  spe- 
cific gravity  of,  12. 

Nervous  System,  a  mechanism,  4  f., 
158  f . ;  chemistry  of,  11  f . ;  elements 
of,  17  f. ;  general  function  of,  31 
f.,  162  f.;  structure  of,  31-68;  the 
sympathetic,  33  f. ;  the  cerebro- 
spinal,  35  f.;  development  of  the, 
107  f. 

Neuroglia,  nature  of,  17. 

Neurokeratin,  13. 

Nuclei  of  nerve-cells,  18;  of  the  me- 
dulla, 50;  of  the  corpus  striatum, 
63  f . ;  of  the  optic  thalami,  64. 

Olives,  the,  47  f.;  functions  of,  156. 

Optic  Thalami,  position  of,  60;  struc- 
ture of,  64  f.;  connections  of,  68; 
development  of,  111  f. ;  functions  of, 
154  f. 

Organ  of  Corti,  97  f. 


504 


INDEX. 


Organs,  kinds  in  nervous  system,  31  f. ; 
the  central,  46  f. ;  functions  of,  135  f. 
Ott,  on  centre  of  temperature,  156. 

Pacini,  corpuscles  of,  78. 

Papillae,  circumvallatae  and  fungi- 
formes,  75  f. 

Peduncles,  of  the  cerebellum,  51;  of 
the  cerebrum,  63  f. 

Perception,  nature  of,  290-360;  nati- 
vistic  and  empiristic  theories  of, 
302  f . ;  by  smell,  305  f. ;  taste,  306  ; 
hearing,  306  f.;  touch,  308  f.;  of 
motion,  313  f . ;  of  temperature, 
314  f.;  of  sight,  322  f.;  of  depth, 
330  f.,  339;  of  spatial  relations, 
330  f.;  development  of,  340  f. 

Pfliiger,  law  of,  127  f. 

Physiological  Psychology,  1  f.;  method 
of,  5  f . ;  claims  of,  9  f . 

Physiology,  relation  to  psychology,  1  f . 

Pia  Mater,  structure  of,  35  f. 

Pons  Varolii,  47 ;  structure  of,  52  f. 

Pressure,  sensations  of,  237  f. ;  spots 
of,  237. 

Preyer,  on  sensitiveness  to  pitch,  247. 

Protagon,  14  f. 

Psychology,  conception  of,  2  f . ;  method 
of,  5  f. 

Psychometry,  method  of,  359  f.;  ele- 
ments of  time  in,  362  f . ;  results  of, 
380. 

Psycho-physics,  method  of,  272  f . ;  of 
sensations  of  touch,  278  f.;  of  sound, 
281  f.;  of  light,  283  f.;  of  smell  and 
taste,  285  f . ;  the  law  of,  362  f. 

Purkinje,  cells  of,  52. 

Pyramidal  tract,  45. 

Quetelet,  on  proportions  of  human 
body,  461. 

Ranvier,  nodes  of,  21  f. 

Reaction-time,  nature  of,  361  f . ;  influ- 
ences upon,  363  f.,  366  f.;  complex 
processes  of,  362  f . 

Reflex  action,  kinds  of,  131 ;  in  spinal 
cord,  135  f.;  conditions  of,  138  f . ; 
in  the  brain,  146  f. 

Regio  olfactoria,  74  f . 

Reissner,  membrane  of,  97. 

Remak,  fibres  of,  20  f . 

Retina,   the,  80;    problem  solved  by, 


82  f.,  87;  layers  of,  87  f.;  nervous 
elements  of,  87  f. ;  rods  and  cones  in, 
88  f.;  own  light  of,  256;  field  of, 
324  f. ;  identical  and  corresponding 
points  of,  332  f. 

Ribot,  on  memory,  424. 

Rolando,  fissure  of,  59,  197  f.,  203  f. 

Schwann,  sheath  and  substance  of,  21  f . 

Sclerotic,  the,  79. 

Seguin,  on  cases  of  aphasia,  220  f. 

Semi-circular  canals,  the,  96. 

Sensations,  end-organs  of,  74-101 ; 
quality  of,  228-270 ;  simple,  228  f .  ; 
conditions  of,  229  f.;  of  smell,  230  f. ; 
of  taste,  234  f . ;  of  temperature,  239 
f . ;  of  pressure,  238  f . ;  the  muscular, 
242  f.;  of  sound,  245  f.;  of  sight, 
254  f . ;  quantity  of,  271  f. ;  measure- 
ment of,  272  f. ;  least  observable 
difference  in,  273  f . ;  range  of,  274  f . ; 
spatial  series  of,  295  f . 

Senses,  organs  of  the,  74-101 ;  classifi- 
cation of  the,  228  f . ;  the  geometrical, 
293  f.;  errors  of  the,  340  f. 

Sight,  end-organs  of,  79  f.;  photo- 
chemistry of,  90  f. ;  sensations  of, 
254  f.;  after-images  of,  263  f.;  ele- 
ments in  perception  of,  322  f.; 
motion  of  eye  in,  329  f.;  single  and 
double  images  in,  333  f . ;  stereoscopic 
and  perspective,  337  f. ;  secondary 
helps  of,  340. 

Smell,  organs  of,  74  f. ;  stimulus  of, 
75;  sensations  of,  230;  kinds  of, 
232  f. ;  measurement  of,  286;  per- 
ceptions of,  305  f . 

Soul,  see  Mind. 

Sound,  analysis  of,  100  f.  ;  sensations 
of,  245  f . ;  kinds  of,  245 ;  nature  of 
the  musical,  246  f . ;  limits  of,  281  f . ; 
direction  of,  306  f. 

Spinal  cord,  membranes  of,  35  f ;  struc- 
ture of,  38  f . ;  fissures  of,  38  f . ;  col- 
umns and  commissures  of,  40 ;  horns 
of,  40;  white  substance  of,  41  f . ; 
gray  substance  of,  43  f . ;  nervous 
tracts  in,  44  f . ;  as  mechanism,  46, 
136  f.;  as  a  central  organ,  137  f. ; 
automatism,  140  f. ;  "centres"  of, 
141  f . ;  excitability  as  a  whole,  142  f . ; 
influence  of  brain  on,  142  f . ;  devel- 
opment of,  107  f . 


INDEX. 


50o 


Starr,  Dr.,  disease  of  cerebellum,  153; 
on  projection  fibres,  222. 

Stimulus,  kinds  of,  117;  heat  as,  124; 
electricity  as,  125  f . ;  of  smell,  230  f . ; 
of  taste,  233  f . ;  of  hearing,  245 ;  of 
sight,  255  f. ;  measurement  of,  272 

^  f . ;  limits  of,  274  f . 

Strieker,  on  common  feeling,  393. 

Substautia  gelatinosa,  41. 

Substantia  nigra,  63. 

Sulci,  of  the  cerebrum,  57  f.;  develop- 
ment of,  113. 

Suspensory  ligament,  function  of,  84  f. 

Sympathetic  System,  structure  of,  33  f. 

Taste,  end-organs  of,  75  f . ;  nerve  of, 
77;  sensations  of,  233  f. ;  stimulus 
of,  234;  kinds  of,  236;  measurement 
of,  285  f . ;  perceptions  of,  306. 

Tegmentum,  see  Crura  Cerebri. 

Temperament,  theory  of,  456  f.;  kinds 
of,  457  f. ;  physical  basis  of,  459  f. 

Temperature,  sensations  of,  239  f. ; 
measurement  of,  280;  after-images 
of,  314 ;  sense  of  locality  by,  314. 

Thalamen-cephalon,  111  f. 

Things,  distinguished  from  sensations, 
290  f. ;  results  of  mental  synthesis, 
293  f.,  304. 

Tones,  the  musical,  245;  pitch  of, 
246  f. ;  sensitiveness  to,  247  f . ;  purity 
of,  248 ;  scale  of,  249  f . ;  relations  of, 
250  f. 


Touch,  end-organs  of,  77  f . ;  sensations 

of,  237  f.;  perceptions  of,  308  f ;  the 

field  of,  308-315. 
Tympanum,    the,    91    f.;    membranes 

of,  92  f.;  windows  of,  92;  office  of, 

93. 

Valli,  principle  of,  122. 

Vestibule,  of  the  ear,  95  f . 

Vitreous  Humor,  the,  81. 

Volkmaun  von  Volkmar,  on  nature  of 
feeling,  386. 

Von  Kries  and  Auerbach,  on  reaction- 
time,  309  f. 

Vulpiau,  on  function  of  optic  thalami, 
155. 

Wagner,  corpuscles  of,  78  f . 

Waller,  method  of,  122. 

Weber,  E.  H.,  241;  law  of,  276  f., 
287J.J  perceptions  of  touch,  308  f.; 
"  sensation -circles  "  of,  309  f. 

Will,  physiological  study  of,  430  f.; 
physical  basis  of,  431  f . ;  effect  of,  on 
bodily  motions,  436  f. ;  in  attention, 
439  f. 

Wundt,  mechanical  theory  of,  172  f. ; 
theory  of  color-sensations,  268, 341  f . ; 
feelings  of  innervation,  405  f. ;  ex- 
pressive movements,  412  f.;  theory 
of  temperament,  458. 

Zonula,  85. 


Typography  by  J.  S.  Gushing  &  Co.,  Boston. 
Presswork  by  Berwick  &  Smith,  Boston. 


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